selftests: forwarding: mirror_gre_bridge_1q_lag: Flush neighbors

After one LAG slave is downed and another upped, it takes a while for
the neighbor on a bridge to time out and get renegotiated. The test does
prompt update of FDB entries by arpinging. But because the neighbor
still references another address, offloading is not possible, and some
packets may end up not being mirrored.

To force the neighbor renegotiation, simply flush the neighbor table at
the bridge.
Signed-off-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/net/forwarding/mirror_gre_bridge_1q_lag.sh

@@ -225,6 +225,7 @@ test_lag_slave()
 
 	# Test connectivity through $up_dev when $down_dev is set down.
 	ip link set dev $down_dev down
+	ip neigh flush dev br1
 	setup_wait_dev $up_dev
 	setup_wait_dev $host_dev
 	$ARPING -I br1 192.0.2.130 -qfc 1