net/mwan3: fix ping issue if last interface recovers from failure

Even though error was fixed the interface checks still fails, if last_resort
was set to blackhole or unreachable.

To fix this issue do not remove failure interface from iptables change on
down event.

Reported-by: Colby Whitney <colby.whitney@luxul.com>
Signed-off-by: Florian Eckert <fe@dev.tdt.de>

net/mwan3/files/etc/hotplug.d/iface/15-mwan3

@@ -59,7 +59,6 @@ case "$ACTION" in
 	;;
 	ifdown)
 		mwan3_delete_iface_rules $INTERFACE
-		mwan3_delete_iface_iptables $INTERFACE
 		mwan3_delete_iface_route $INTERFACE
 		mwan3_delete_iface_ipset_entries $INTERFACE
 		mwan3_track_signal $INTERFACE $DEVICE

net/mwan3/files/usr/sbin/mwan3

@@ -37,6 +37,7 @@ ifdown()
 	ACTION=ifdown INTERFACE=$1 /sbin/hotplug-call iface
 
 	kill $(pgrep -f "mwan3track $1 $2") &> /dev/null
+	mwan3_delete_iface_iptables $1
 	mwan3_track_clean $1
 }