selftests: forwarding: mirror_gre_bridge_1q_lag: Enable forwarding

This test relies on routing in the primary traffic path, but neglects to
enable forwarding. Do so.

Signed-off-by: Petr Machata <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

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

···
 	h4_create
 	switch_create
 
+	forwarding_enable
+
 	trap_install $h3 ingress
 	trap_install $h4 ingress
 }
···
 
 	trap_uninstall $h4 ingress
 	trap_uninstall $h3 ingress
+
+	forwarding_restore
 
 	switch_destroy
 	h4_destroy