[][Add auto hook toggling for pptp/l2tp]

[Description]
Add a script to automatically enable/disable HNAT hooks
because HNAT cannot support pptp/l2tp protocol.
    - when pptp/l2tp interface is up -> disable hnat
    - when pptp/l2tp interface is down -> enable hnat

[Release-log]
N/A

Change-Id: Icb0bafc5750522aae921d062334fe18345ba630f
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/4731853
1 file changed