pending changes for TOE support

After review by Mike Silbersack I've committed the hooks that provide
a driver independent interface to TCP offload.

I would like to commit the changes to tcp_subr.c and tcp_usrreq.c to
actually make use of the new interface. Please review the following:

http://www.fsmware.com/freebsd/tcp/tcp_subr.c.diff

http://www.fsmware.com/freebsd/tcp/tcp_usrreq.c.diff

The new KPI is provided by the following 2 files:
http://www.fsmware.com/freebsd/tcp/tcp_ofld.c
http://www.fsmware.com/freebsd/tcp/tcp_ofld.h


Thank you for taking the time to review and provide feedback.

-Kip