tcp: change SOCKBUF_* macros to SOCK_[RECV|SEND]BUF_* macros
Change the older LOCK related macros over to the
dedicated send/recv buffer macros in the base tcp stack.
No functional change intended.
Reviewed By: tuexen, transport
Sponsored by: NetApp, Inc.
Differential Revision: https://reviews.freebsd.org/D47567