Improve debugging

Wrap the run time deubg option in a compile time option. (DEBUG)

Merge gnns changes to make the debug mode run time selectable.

First cut at making debug mode run time selectable

On FreeBSD IPv6 sockets have the IPV6_V6ONLY option enabled by
default. To allow the scripts to select the address family
via the --ip_version option transparently, disable the
IPV6_V6ONLY option implicilty on all sockets.
This fixes #132.

Sponsored by:	Netflix, Inc.

Fix remote mode

This fixes #114 and also the TCP remote mode.

Sync with nplab/packetdrill

Sponsored by:	Netflix, Inc.

Sponsored by:	Netflix, Inc.

Sync from nplab/packetdrill

Merge pull request #1 from nplab/master

This is based on a patch from Jason Eggleston with minor modifications
from me.

See https://github.com/google/packetdrill/commit/47582211690ffc2a7f40c371c19d283b2df26a44#diff-9b9398b17ceeb5025735f4c20d63a3e5L547

Improve timing and fix a race condition

used by it.

Sponsored by:	Netflix

Sponsored by: Netflix

When injecting out of the blue packet, don't update the socket under test
if one is available. This allows to use the python code for TCP info to
inspect closed sockets.

Sponsored by:	Netflix.

Sponsored by:	Netflix

Add support for SCTP_PR_SCTP_RTX symbol on freebsd.

Sponsored by:	Netflix