Allow fcntl F_SETLK on sockets.

Addresses denials such as:
type=1400 : avc: denied { lock } for comm="PushCheckSendS" path="socket:[1834573]" dev="sockfs" ino=X scontext=u:r:untrusted_app:s0 tcontext=u:r:untrusted_app:s0 tclass=tcp_socket

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>

(cherry picked from commit 2c759185)

Bug: 18730521
Change-Id: Ie68955c26ddedb3acd7b7aa18afbf8b35c2c2f78