patches/openwrt: conntrack: disable checksum

For some unknown reason, it does not acquire prefix
via DHCPv6-PD and/or renew the prefix.

Let's disable checksum for now.

Bug report:
https://forum.turris.cz/t/dhcpv6-on-wan-not-working-tos-5-pppoe/12853?u=pepe

patches/openwrt/branding/0003-nf-conntrack-improve-default-values.patch

@@ -26,7 +26,7 @@ index 37baf5fd6f..bcd730d470 100644
 -net.netfilter.nf_conntrack_checksum=0
 -net.netfilter.nf_conntrack_max=16384
 -net.netfilter.nf_conntrack_tcp_timeout_established=7440
-+net.netfilter.nf_conntrack_checksum=1
++net.netfilter.nf_conntrack_checksum=0
 +net.netfilter.nf_conntrack_max=262144
 +net.netfilter.nf_conntrack_tcp_timeout_established=432000
  net.netfilter.nf_conntrack_udp_timeout=60