selftests/net: Fix broken test case in psock_fanout

The error return falue form sock_fanout_open is -1, not zero. One test
case was checking for 0 instead of -1.

Tested: Built and tested in clean client.
Signed-off-by: Mike Maloney <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

tools/testing/selftests/net/psock_fanout.c

···
 		exit(1);
 	}
 
-	if (sock_fanout_open(PACKET_FANOUT_CPU, first_group_id)) {
+	if (sock_fanout_open(PACKET_FANOUT_CPU, first_group_id) != -1) {
 		fprintf(stderr, "ERROR: joined group with wrong type.\n");
 		exit(1);
 	}