[NETLINK]: don't reinitialize callback mutex

Don't reinitialize the callback mutex the netlink_kernel_create caller
handed in, it is supposed to already be initialized and could already
be held by someone.
Signed-off-by: NPatrick McHardy <kaber@trash.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/netlink/af_netlink.c

@@ -388,8 +388,12 @@ static int __netlink_create(struct socket *sock, struct mutex *cb_mutex,
 	sock_init_data(sock, sk);
 
 	nlk = nlk_sk(sk);
-	nlk->cb_mutex = cb_mutex ? : &nlk->cb_def_mutex;
+	if (cb_mutex)
+		nlk->cb_mutex = cb_mutex;
+	else {
+		nlk->cb_mutex = &nlk->cb_def_mutex;
 		mutex_init(nlk->cb_mutex);
+	}
 	init_waitqueue_head(&nlk->wait);
 
 	sk->sk_destruct = netlink_sock_destruct;