[][kernel][common][firewall][Add PPTP helper rule to fix PPTP VPN feature by default]

[Description]
Add PPTP helper rule to fix PPTP VPN feature by default.
In patch as below, linux kernel disable automatic helper
assignment by default for security reasons. (nf_conntrack_helper=0)
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
/commit/?h=linux-4.9.y&id=8f9872be6db939a75a075cd893a47ce5742cee00
Instead of turning on nf_conntrack_helper,it suggests to use the
iptables CT target to attach helpers.

[Release-log]
N/A

Change-Id: I7e3260024bad00486b0e16406e813c372910fc38
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/6712515
1 file changed