usleep() might be overshooting substantially in that case.

When enabled, no final TCP RST segment or SCTP ABORT chunk is sent
to cleanup the state at the SUT.

The assert() calls clarify and ensure which thread the functions
is allowed to run in.

Ensure that
 0.00 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+1.00 close(3) = -1
      `echo Cleanup`
works

This is ported from packetdrill 2.0.

When using local mode on *BSD, using the tun0 device was hard
coded in contrast to Linux, where the next unused tun device
was used.
This patch changes the behaviour on *BSD to use the next unused
tun device. This also requires that the device is removed when
packetdrill terminates. This was the case on Linux, but not on
*BSD.
On *BSD there is also a new command line option (--tun-dev) to
set the device name and not select an ephemerial one.

Sponsored by: Netflix

When a blocking system call is ongoing, the error message shown was
wrong. It was indicated that a blocking system call is on-going when
the program terminates. This is correct, but hides the error message
which describes why packetdrill is terminating.

Sponsored by:	Netflix

FreeBSD supports usleep(), so use it.
Sonsored by Netflix.

This fixes a bug on non-Linux system for the handling of
blocking system calls. While waiting, release the state
mutex.
Sponsored by Netflix.

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>