LRO: Don't merge ACK and non-ACK packets together

[rstone]

Summary

LRO was willing to merge ACK and non-ACK packets together. This
can cause incorrect th_ack values to be reported up the stack.
While non-ACKs are quite unlikely to appear in practice, LRO's
behaviour is against the spec. Make LRO unwilling to merge
packets with different TH_ACK flag values in order to fix the
issue.

Found by: Sysunit test

Test Plan

This unit test fails without the fix:
https://github.com/rysto32/freebsd/blob/sysunit/tests/sys/sysunit/tcp_lro_test.cc#L573

$ ./tcp_lro --gtest_filter=*TestNonAck
Running main() from /srcpool/src/rstone/worktree/sysunit/contrib/googletest/googletest/src/gtest_main.cc
Note: Google Test filter = *TestNonAck
[==========] Running 2 tests from 2 test cases.
[----------] Global test environment set-up.
[----------] 1 test from TcpLroTestSuite/0, where TypeParam = IPv4
[ RUN      ] TcpLroTestSuite/0.TestNonAck
unknown file: Failure

Unexpected mock function call - returning directly.
    Function call: if_input(0x15c4d634d000)
Google Mock tried the following 2 expectations, but none matched:

/srcpool/src/rstone/worktree/sysunit/tests/sys/sysunit/tcp_lro_test.cc:600: tried expectation #0: EXPECT_CALL(*this->mockIfp, if_input(PacketMatcher(pkt1)))...
  Expected arg #0: Ethernet/IPv4/TCP/Payload
           Actual: 0x15c4d634d000, IPv4: ip_len field is 54 (expected 47)
         Expected: to be called once
           Actual: never called - unsatisfied and active
/srcpool/src/rstone/worktree/sysunit/tests/sys/sysunit/tcp_lro_test.cc:603: tried expectation #1: EXPECT_CALL(*this->mockIfp, if_input(PacketMatcher(pkt2)))...
  Expected arg #0: Ethernet/IPv4/TCP/Payload
           Actual: 0x15c4d634d000, IPv4: ip_len field is 54 (expected 47)
         Expected: to be called once
           Actual: never called - unsatisfied and active
/srcpool/src/rstone/worktree/sysunit/tests/sys/sysunit/tcp_lro_test.cc:600: Failure
Actual function call count doesn't match EXPECT_CALL(*this->mockIfp, if_input(PacketMatcher(pkt1)))...
         Expected: to be called once
           Actual: never called - unsatisfied and active
/srcpool/src/rstone/worktree/sysunit/tests/sys/sysunit/tcp_lro_test.cc:603: Failure
Actual function call count doesn't match EXPECT_CALL(*this->mockIfp, if_input(PacketMatcher(pkt2)))...
         Expected: to be called once
           Actual: never called - unsatisfied and active
[  FAILED  ] TcpLroTestSuite/0.TestNonAck, where TypeParam = IPv4 (1 ms)
[----------] 1 test from TcpLroTestSuite/0 (1 ms total)

[----------] 1 test from TcpLroTestSuite/1, where TypeParam = IPv6
[ RUN      ] TcpLroTestSuite/1.TestNonAck
unknown file: Failure

Unexpected mock function call - returning directly.
    Function call: if_input(0x15c4d634d200)
Google Mock tried the following 2 expectations, but none matched:

/srcpool/src/rstone/worktree/sysunit/tests/sys/sysunit/tcp_lro_test.cc:600: tried expectation #0: EXPECT_CALL(*this->mockIfp, if_input(PacketMatcher(pkt1)))...
  Expected arg #0: Ethernet/IPv6/TCP/Payload
           Actual: 0x15c4d634d200, IPv6: ip6_plen field is 34 (expected 27)
         Expected: to be called once
           Actual: never called - unsatisfied and active
/srcpool/src/rstone/worktree/sysunit/tests/sys/sysunit/tcp_lro_test.cc:603: tried expectation #1: EXPECT_CALL(*this->mockIfp, if_input(PacketMatcher(pkt2)))...
  Expected arg #0: Ethernet/IPv6/TCP/Payload
           Actual: 0x15c4d634d200, IPv6: ip6_plen field is 34 (expected 27)
         Expected: to be called once
           Actual: never called - unsatisfied and active
/srcpool/src/rstone/worktree/sysunit/tests/sys/sysunit/tcp_lro_test.cc:600: Failure
Actual function call count doesn't match EXPECT_CALL(*this->mockIfp, if_input(PacketMatcher(pkt1)))...
         Expected: to be called once
           Actual: never called - unsatisfied and active
/srcpool/src/rstone/worktree/sysunit/tests/sys/sysunit/tcp_lro_test.cc:603: Failure
Actual function call count doesn't match EXPECT_CALL(*this->mockIfp, if_input(PacketMatcher(pkt2)))...
         Expected: to be called once
           Actual: never called - unsatisfied and active
[  FAILED  ] TcpLroTestSuite/1.TestNonAck, where TypeParam = IPv6 (0 ms)
[----------] 1 test from TcpLroTestSuite/1 (0 ms total)

[----------] Global test environment tear-down
[==========] 2 tests from 2 test cases ran. (1 ms total)
[  PASSED  ] 0 tests.
[  FAILED  ] 2 tests, listed below:
[  FAILED  ] TcpLroTestSuite/0.TestNonAck, where TypeParam = IPv4
[  FAILED  ] TcpLroTestSuite/1.TestNonAck, where TypeParam = IPv6

 2 FAILED TESTS

It passes with the fix:

$ ./tcp_lro --gtest_filter=*TestNonAck
Running main() from /srcpool/src/rstone/worktree/sysunit/contrib/googletest/googletest/src/gtest_main.cc
Note: Google Test filter = *TestNonAck
[==========] Running 2 tests from 2 test cases.
[----------] Global test environment set-up.
[----------] 1 test from TcpLroTestSuite/0, where TypeParam = IPv4
[ RUN      ] TcpLroTestSuite/0.TestNonAck
[       OK ] TcpLroTestSuite/0.TestNonAck (1 ms)
[----------] 1 test from TcpLroTestSuite/0 (1 ms total)

[----------] 1 test from TcpLroTestSuite/1, where TypeParam = IPv6
[ RUN      ] TcpLroTestSuite/1.TestNonAck
[       OK ] TcpLroTestSuite/1.TestNonAck (0 ms)
[----------] 1 test from TcpLroTestSuite/1 (0 ms total)

[----------] Global test environment tear-down
[==========] 2 tests from 2 test cases ran. (1 ms total)
[  PASSED  ] 2 tests.

[rstone]

Ping? I'd like to get this off of my queue by some time next week.

[tuexen]

I'll bring it up on the transport call tomorrow.