Crash due to mutex genl_lock called from RCU context

Grabbing the mutex should not be done from netlink_sock_destruct() but
from netlink_release()

CRs-Fixed: 1094434
Change-Id: I69ae0d8589a0878b9758619893848afc272179c5
Signed-off-by: Eric Dumazet <edumazet@google.com>
Patch-mainline: linux-netdev @ 11/26/16, 04:54
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>