packet: fix race condition in packet_set_ring

commit 5a01eaf1 ("packet: fix race condition
in packet_set_ring") was incorrectly resolved.
Add the missing lock_sock(sk) and release_sock(sk) calls.

Change-Id: I6565bf3e3c6a15d6f1b93cab0536424dbacb187b
Signed-off-by: Srinivasa Rao Kuppala <srkupp@codeaurora.org>