v1.53.0 — icmp-type-unknown

New linter smell icmp-type-unknown (63 smells, error): a named --icmp-type/--icmpv6-type (nft icmp/icmpv6 type) the tools don't recognise, or a numeric type over 255, is refused at load — a hand file with a typo boots with no firewall. Measured (iptables/ip6tables 1.8.13, nft 1.1.6): Unknown ICMP type, Could not parse ICMP type. Names checked against the union of iptables+nft vocabularies (so nd-neighbor-solicit and neighbour-solicitation both pass), case-insensitive. Two samples. Tests 331. (#74)