net/core: add lock context change annotations in net/core/sock.c

__lock_sock() and __release_sock() releases and regrabs lock but
were missing proper annotations. Add it. This removes following
warning from sparse. (Currently __lock_sock() does not emit any
warning about it but I think it is better to add also.)

 net/core/sock.c:1580:17: warning: context imbalance in '__release_sock' - unexpected unlock
Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/sock.c

@@ -1557,6 +1557,8 @@ struct sk_buff *sock_alloc_send_skb(struct sock *sk, unsigned long size,
 EXPORT_SYMBOL(sock_alloc_send_skb);
 
 static void __lock_sock(struct sock *sk)
+	__releases(&sk->sk_lock.slock)
+	__acquires(&sk->sk_lock.slock)
 {
 	DEFINE_WAIT(wait);
 
@@ -1573,6 +1575,8 @@ static void __lock_sock(struct sock *sk)
 }
 
 static void __release_sock(struct sock *sk)
+	__releases(&sk->sk_lock.slock)
+	__acquires(&sk->sk_lock.slock)
 {
 	struct sk_buff *skb = sk->sk_backlog.head;