net: add missing READ_ONCE(sk->sk_rcvlowat) annotation

In a prior commit, I forgot to change sk_getsockopt()
when reading sk->sk_rcvlowat locklessly.

Fixes: eac66402 ("net: annotate sk->sk_rcvlowat lockless reads")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/sock.c

@@ -1730,7 +1730,7 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
 		break;
 
 	case SO_RCVLOWAT:
-		v.val = sk->sk_rcvlowat;
+		v.val = READ_ONCE(sk->sk_rcvlowat);
 		break;
 
 	case SO_SNDLOWAT: