selftests: forwarding: mirror_gre_changes: Fix waiting for neighbor

When running the test on soft devices, there's no mechanism to
gratuitously start resolving the neighbor for remote tunnel endpoint.
So instead of passively waiting, wait for the device to be up, and then
probe the neighbor with a ping.

Signed-off-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/net/forwarding/mirror_gre_changes.sh

@@ -122,15 +122,8 @@ test_span_gre_egress_up()
 	# After setting the device up, wait for neighbor to get resolved so that
 	# we can expect mirroring to work.
 	ip link set dev $swp3 up
-	while true; do
-		ip neigh sh dev $swp3 $remote_ip nud reachable |
-		    grep -q ^
-		if [[ $? -ne 0 ]]; then
-			sleep 1
-		else
-			break
-		fi
-	done
+	setup_wait_dev $swp3
+	ping -c 1 -I $swp3 $remote_ip &>/dev/null
 
 	quick_test_span_gre_dir $tundev ingress
 	mirror_uninstall $swp1 ingress