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>
diff --git a/net/core/sock.c b/net/core/sock.c
index d9eec15..bbb25be 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -631,7 +631,7 @@
 
 	case SO_TIMESTAMPING:
 		if (val & ~SOF_TIMESTAMPING_MASK) {
-			ret = EINVAL;
+			ret = -EINVAL;
 			break;
 		}
 		sock_valbool_flag(sk, SOCK_TIMESTAMPING_TX_HARDWARE,