The goal here is to be able to route a prefix of user-configurable
size over the tun device or to the remote packetdrill server, so that
tests can use more than one remote IP. The immediate motivation is
testing GRE, where there is a remote IP for the TCP endpoint and a
separate remote IP for the GRE decapsulator.

Change-Id: I36b7025a242c3803802087c91d284a41c62ca1bd

Initial commit for the packetdrill network stack testing tool:

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



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