selftests: forwarding: no_forwarding: Down ports on cleanup

This test neglects to put ports down on cleanup. Fix it.

Fixes: 476a4f05 ("selftests: forwarding: add a no_forwarding.sh test")
Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/0baf91dc24b95ae0cadfdf5db05b74888e6a228a.1724430120.git.petrm@nvidia.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

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

@@ -233,6 +233,9 @@ cleanup()
 {
 	pre_cleanup
 
+	ip link set dev $swp2 down
+	ip link set dev $swp1 down
+
 	h2_destroy
 	h1_destroy