nat66: T4586: Add SNAT destination prefix and DNAT address

[sever-sever]

Change Summary

Ability to configure SNAT destination prefix and
DNAT source address
Add option "!" - not address/prefix for NAT66

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

• https://phabricator.vyos.net/T4586

Component(s) name

nat66

Proposed changes

How to test

Nat configuration:

set nat66 source rule 10 destination prefix '2001:db8::2/128'
set nat66 source rule 10 outbound-interface 'eth1'
set nat66 source rule 10 source prefix '2001:db8:1111::/64'
set nat66 source rule 10 translation address 'masquerade'

set nat66 source rule 20 destination prefix '!2001:db8::6/127'
set nat66 source rule 20 outbound-interface 'eth1'
set nat66 source rule 20 source prefix '2001:db8:1111::/64'
set nat66 source rule 20 translation address 'masquerade'

set nat66 destination rule 10 destination address '2001:db8:1111::/64'
set nat66 destination rule 10 inbound-interface 'eth1'
set nat66 destination rule 10 source address '!2001:db8::6/127'
set nat66 destination rule 10 translation address '2001:db8::444'

Nftables:

vyos@r14# sudo nft list table ip6 nat
table ip6 nat {
	chain PREROUTING {
		type nat hook prerouting priority dstnat; policy accept;
		iifname "eth1" counter packets 1 bytes 166 ip6 saddr != 2001:db8::6/127 ip6 daddr 2001:db8:1111::/64 dnat to 2001:db8::444 comment "DST-NAT66-10"
	}

	chain POSTROUTING {
		type nat hook postrouting priority srcnat; policy accept;
		oifname "eth1" counter packets 0 bytes 0 ip6 saddr 2001:db8:1111::/64 ip6 daddr 2001:db8::2 masquerade comment "SRC-NAT66-10"
		oifname "eth1" counter packets 0 bytes 0 ip6 saddr 2001:db8:1111::/64 ip6 daddr != 2001:db8::6/127 masquerade comment "SRC-NAT66-20"
	}
...
}

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly