net: add missing data-race annotation for sk_ll_usec

In a prior commit I forgot that sk_getsockopt() reads
sk->sk_ll_usec without holding a lock.

Fixes: 0dbffbb5 ("net: annotate data race around sk_ll_usec")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/sock.c

@@ -1900,7 +1900,7 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
 
 #ifdef CONFIG_NET_RX_BUSY_POLL
 	case SO_BUSY_POLL:
-		v.val = sk->sk_ll_usec;
+		v.val = READ_ONCE(sk->sk_ll_usec);
 		break;
 	case SO_PREFER_BUSY_POLL:
 		v.val = READ_ONCE(sk->sk_prefer_busy_poll);