net: use proper lockdep annotation in __sk_dst_set()

__sk_dst_set() must be called while we own the socket.

We can get proper lockdep coverage using lockdep_sock_is_held()
and rcu_dereference_protected()
Signed-off-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -1780,11 +1780,8 @@ __sk_dst_set(struct sock *sk, struct dst_entry *dst)
 
 	sk_tx_queue_clear(sk);
 	sk->sk_dst_pending_confirm = 0;
-	/*
-	 * This can be called while sk is owned by the caller only,
-	 * with no state that can be checked in a rcu_dereference_check() cond
-	 */
-	old_dst = rcu_dereference_raw(sk->sk_dst_cache);
+	old_dst = rcu_dereference_protected(sk->sk_dst_cache,
+					    lockdep_sock_is_held(sk));
 	rcu_assign_pointer(sk->sk_dst_cache, dst);
 	dst_release(old_dst);
 }