VoIP behind a OpenWrt NAT router

[mpa]

@Ultrazauberer

I can't establish phone connections to some numbers of my callers. Sometimes I can't even here a free line signal on some phone numbers. And sometimes I can hear the ring signal and when the call is answered the connection can't establish.

The following changes on the router (OpenWrt 18.06.1) made VoIP work for me:

• install the kmod-nf-nathelper-extra package
• increase the net.netfilter.nf_conntrack_expect_max sysctl parameter to 16