Improve TCP state change reporting via dtrace

[tuexen]

Summary

When using dtrace to watch TCP state changes, not all transitions are caught.
The problem can be reproduced by running the dtrace script tcpstate.d while executing the packetdrill script close-wait-ipv4.pkt.

Without the patch, tcpstate.d reports while running close-wait-ipv4.pkt:

CPU    DELTA(us) CID                OLD                     NEW                  TIMESTAMP
  1 101368577164 fffff8002957ecb0   state-closed         -> state-listen         101368577164931
  1 101368578541 fffff800294bcae0   state-closed         -> state-syn-sent       101368578541920
  1       107461 fffff800294bcae0   state-syn-sent       -> state-established    101368686003429
  1       108026 fffff800294bcae0   state-established    -> state-close-wait     101368794029659
  1       107957 fffff800294bcae0   state-close-wait     -> state-last-ack       101368901986890

The state changes from state-listen to state-closed and from state-last-ack to state-closed are missing.

With the patch the corresponding output is

CPU    DELTA(us) CID                OLD                     NEW                  TIMESTAMP
  3  33306868592 fffff800cfc173a0   state-closed         -> state-listen         33306868592543
  3  33306880517 fffff800cfc161d0   state-closed         -> state-syn-sent       33306880517424
  3       118265 fffff800cfc161d0   state-syn-sent       -> state-established    33306998782931
  3       117745 fffff800cfc161d0   state-established    -> state-close-wait     33307116528533
  3       118165 fffff800cfc161d0   state-close-wait     -> state-last-ack       33307234694066
  3       117779 fffff800cfc161d0   state-last-ack       -> state-closed         33307352473996
  3       647722 fffff800cfc173a0   state-listen         -> state-closed         33307516315376

which shows these state changes.

[tuexen]

Same changes, but diff based on r308776.