Add regression test for D27164

[jtl]

Summary

D27164 describes a problem with (and fix for) implicit local port selection as part of the connect() call. This regression test fails for IPv6 without the fix and passes with the fix.

Test Plan

Run the regression test with and without the fix. Verify the test fails without the fix and passes with the fix.

Without the fix:

sys/netinet/tcp_connect_port_test:basic_ipv4  ->  passed  [2.093s]
sys/netinet/tcp_connect_port_test:basic_ipv6  ->  failed: /home/ec2-user/ocafirmware/FreeBSD/tests/sys/netinet/tcp_connect_port_test.c:245: client socket 55535 using the same port as server  [1.972s]

With the fix:

sys/netinet/tcp_connect_port_test:basic_ipv4  ->  passed  [2.109s]
sys/netinet/tcp_connect_port_test:basic_ipv6  ->  passed  [2.486s]