Fix error return for setsockopt(SO_TIMESTAMPING)

I guess it should be -EINVAL rather than EINVAL. I have not checked
when the bug came in. Perhaps a candidate for -stable?
Signed-off-by: Rémi Denis-Courmont <remi.denis-courmont@nokia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/sock.c

@@ -631,7 +631,7 @@ set_rcvbuf:
 
 	case SO_TIMESTAMPING:
 		if (val & ~SOF_TIMESTAMPING_MASK) {
-			ret = EINVAL;
+			ret = -EINVAL;
 			break;
 		}
 		sock_valbool_flag(sk, SOCK_TIMESTAMPING_TX_HARDWARE,