- Add IPv6 router dispatch to AddOutputDNAT/RemoveOutputDNAT in both
nftables and iptables managers (was hardcoded to v4 router only).
- Fix all DNAT and AddDNATRule dispatch methods to check Is6() first,
then error with ErrIPv6NotInitialized if v6 components are missing.
Previously the hasIPv6() && Is6() pattern silently fell through to
the v4 router for v6 addresses when v6 was not initialized.
- Add ErrIPv6NotInitialized sentinel error, replace all ad-hoc
"IPv6 not initialized" format strings across both managers.
- Rename sourcePort/targetPort to originalPort/translatedPort in all
DNAT method signatures to reflect actual DNAT semantics.
- Remove stale "localAddr must be IPv4" comments from interface.
2f5d9fc0cd