ctl: use socket buffer mutexes in struct socket directly

A mechanical change performed with sed(1) script:

s/SOCKBUF_LOCK\(&so->so_rcv\)/SOCK_RECVBUF_LOCK(so)/
s/SOCKBUF_UNLOCK\(&so->so_rcv\)/SOCK_RECVBUF_UNLOCK(so)/
s/SOCKBUF_MTX\(&so->so_rcv\)/SOCK_RECVBUF_MTX(so)/
s/SOCKBUF_LOCK\(&so->so_snd\)/SOCK_SENDBUF_LOCK(so)/
s/SOCKBUF_UNLOCK\(&so->so_snd\)/SOCK_SENDBUF_UNLOCK(so)/
s/SOCKBUF_MTX\(&so->so_snd\)/SOCK_SENDBUF_MTX(so)/

Reviewed by: mav
Differential Revision: https://reviews.freebsd.org/D45190