tcp: Mbuf leak while holding a socket buffer lock.

When running at NF the current Rack and BBR changes with the recent
commits from Richard that cause the socket buffer lock to be held over
the ip_output() call and then finally culminating in a call to tcp_handle_wakeup()
we get a lot of leaked mbufs. I don't think that this leak is actually caused
by holding the lock or what Richard has done, but is exposing some other
bug that has probably been lying dormant for a long time. I will continue to
look (using his changes) at what is going on to try to root cause out the issue.

In the meantime I can't leave the leaks out for everyone else. So this commit
will revert all of Richards changes and move both Rack and BBR back to just
doing the old sorwakeup_locked() calls after messing with the so_rcv buffer.

We may want to look at adding back in Richards changes after I have pinpointed
the root cause of the mbuf leak and fixed it.

Reviewed by: mtuexen,rscheff
Sponsored by: Netflix Inc
Differential Revision: https://reviews.freebsd.org/D30704

(cherry picked from commit 67e892819b26c198e4232c7586ead7f854f848c5)