mwan3: refine link selection

- globals src_ip to none
 - ip route back to source
 - add mwan3rtmon
 - update version to 2.7

Signed-off-by: Chen Minqiang <ptpt52@gmail.com>

net/mwan3/files/etc/config/mwan3

@@ -1,7 +1,7 @@
 
 config globals 'globals'
 	option mmx_mask '0x3F00'
-	option local_source 'lan'
+	option local_source 'none'
 
 config interface 'wan'
 	option enabled '1'

net/mwan3/files/etc/hotplug.d/iface/16-mwan3

@@ -0,0 +1,17 @@
+#!/bin/sh
+
+. /lib/functions.sh
+. /lib/functions/network.sh
+. /lib/mwan3/mwan3.sh
+
+config_load mwan3
+config_get_bool enabled globals 'enabled' '0'
+[ ${enabled} -gt 0 ] || exit 0
+
+if [ "$ACTION" == "ifup" ]; then
+	mwan3_lock
+	mwan3_rtmon
+	mwan3_unlock
+fi
+
+exit 0