Change the SOCKBUF_LOCK calls to use the more refined SOCK_XXXBUF_LOCK/UNLOCK.

The socket buffer locking used to be standard on SOCKBUF_LOCK/UNLOCK. But we are now
moving to a more elegant SOCK_SENDBUF_LOCK/UNLOCK and SOCK_RECVBUF_LOCK/UNLOCK.
Lets get BBR and Rack to use these updated macros.

Reviewed by:glebius, tuexen, rscheff
Differential Revision:https://reviews.freebsd.org/D47542