Every time restart firewall, pptpd.include will be executed. Thus two ppp policy will be added to forwarding_rule chain.
Modified to delete old policies before add new ones.
P.S. according to https://wiki.openwrt.org/doc/howto/vpn.server.pptpd , ppp+ policies will also allow data from other ppp interfaces, including pppoe. Thus if you are using ppp (PPPoE or similar) in wan(that's what in my case), this configuration is insecure. However someone made it like this: https://datahunter.org/openwrt_pptp
