feat(ns-api): redirects, show all supported protocols

[gsanchietti]

Return all protocols from /etc/protocols

#1069

From manual, the proto field supports the following:

Match incoming traffic using the given protocol. Can be one (or several when using list syntax) of tcp, udp, udplite, icmp, esp, ah, sctp, or all or it can be a numeric value, representing one of these protocols or a different one. A protocol name from /etc/protocols is also allowed. The number 0 is equivalent to all.

See https://openwrt.org/docs/guide-user/firewall/firewall_configuration