MFC r345262:
Modify struct nat64_config. Add second IPv6 prefix to generic config structure and rename another fields to conform to RFC6877. Now it contains two prefixes and length: PLAT is provider-side translator that translates N:1 global IPv6 addresses to global IPv4 addresses. CLAT is customer-side translator (XLAT) that algorithmically translates 1:1 IPv4 addresses to global IPv6 addresses. Use PLAT prefix in stateless (nat64stl) and stateful (nat64lsn) translators. Modify nat64_extract_ip4() and nat64_embed_ip4() functions to accept prefix length and use plat_plen to specify prefix length. Retire net.inet.ip.fw.nat64_allow_private sysctl variable. Add NAT64_ALLOW_PRIVATE flag and use "allow_private" config option to configure this ability separately for each NAT64 instance. Obtained from: Yandex LLC Sponsored by: Yandex LLC