Only send the cleanup messages when the socket is not in a front state.
This fixes a bug where in case of the SUT being a server was sent
a TCP RST with wildcard addresses and ports.

Current limitations:
* Chunk parameters are not yet supported.
* Error causes are not yet supported.
* Chunks can't be bundled with COOKIE-ECHO chunks.
* Chunk flags are not supported.
* Chunk lengths are not supported.
* Gap reports and duplicate TSNs are not supported for SACK chunks.
* SCTP related ICMP messages are not supported.
This version is only tested in a limited way, only on FreeBSD and
only in local mode.

Initial commit for the packetdrill network stack testing tool:

  https://code.google.com/p/packetdrill/



Signed-off-by: Neal Cardwell <ncardwell@google.com>