luci-app-firewall: sync protocol list with musl libc

[R41D1]

Summary

• Remove 23 protocol names from the firewall protocol list that musl's getprotobyname() cannot resolve

nftables resolves symbolic protocol names via getprotobyname(). On musl (used by all OpenWrt targets), this function only knows a hardcoded subset of 36 protocols (src/network/proto.c). musl intentionally does not read /etc/protocols.

When LuCI writes a symbolic name like vrrp to /etc/config/firewall, nftables fails with Could not resolve protocol name on rule load, breaking the entire firewall.

The protocol list was originally sourced from a glibc-based /etc/protocols. This patch syncs it to only include names musl can resolve. Users who need removed protocols (e.g. VRRP=112, SCTP=132) can still enter them by number.

Removed protocols: hopopt, igp, dccp, icmpv6 (alias; ipv6-icmp stays), eigrp, ax.25, etherip, ipcomp, vrrp, l2tp, isis, sctp, fc, mh, ipv6-mh, mobility-header, udplite, mpls-in-ip, manet, hip, shim6, wesp, rohc, duplicate rspf/CPHB alias.

Test plan

• Create firewall rule with protocol tcp — rule saves and firewall loads
• Create firewall rule with protocol number 112 — rule saves and firewall loads
• Verify vrrp no longer appears in protocol dropdown (prevents the nftables failure)
• service firewall restart succeeds with all selectable protocols

Fixes #8449

🤖 Generated with Claude Code

[R41D1]

Closing in favor of the approach from the issue discussion — adding a musl-compatibility flag (4th field) to each protocol entry and converting unsupported names to numeric values on write via protoToNum(). That preserves the full protocol list for user reference while ensuring nftables always gets resolvable values. Strictly better than removing entries.