T7485: ia-na ipv6 for PPPoE link

[nvandamme]

Change summary

If a pppoe interface define ipv6 address autoconf, this interface doesn't register the provided IA-NA address from RA's/DHPCv6 announces (dhcp6c).

By modifying the dhcp6c configuration template and handling pppoe interfaces edge cases, the right ia-na entry can be written and handled by dhcp6c to the pppoe interface.

See : https://vyos.dev/T7485#234216

NOTE

It doesn't handle requesting a specific IA-NA address (send ia_na is always defaulting to 0).
Is a new parameter in interfaces pppoe [pppoeN] ipv6 xml definition should be handled has well?

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://vyos.dev/T7485

Related PR(s)

How to test / Smoketest result

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

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• CLI Smoketests (no interfaces) 👍 passed
• CLI Smoketests VPP 👍 passed
• CLI Smoketests (interfaces only) 👍 passed
• Config tests 👍 passed
• Config tests VPP 👍 passed
• RAID1 tests 👍 passed
• TPM tests 👍 passed

[c-po]

Please try if it is possible to drop the entire line 8

[nvandamme]

• (address is vyos_defined and 'dhcpv6' in address) might be removed because the user explicitly expects to have an ipv6 address provided by dhcpv6 for common interfaces.

• the removal of (ipv6 is vyos_defined and ipv6.address is vyos_defined and 'dhcpv6' in ipv6.address) will always provide an IA_NA address to the user when dhcpv6-pd is setup on a pppoe interface: leaving this part ensure the user have the choice to request an ipv6 address for the pppoe interface with or without dhcpv6-pd and vice-versa.

I very much prefer to leave this line (and line 29) as it is proposed on commit e0cefe0, because it is specifically handling these scenarios:

• requesting explicitly an ipv6 via dhcpv6 on a common interface (not pppoe) via set interface type name address dhcpv6
• requesting explicitly an ipv6 via dhcpv6 on a pppoe interface independently of any dhcpv6-pd configuration via set interface pppoe pppoeN ipv6 address dhcpv6
• requesting explicitly dhcpv6-pd on a pppoe interface without requesting a dedicated ipv6 for this pppoe interface.

Note: set interface type name dhcpv6-options temporary is not explicit and might be confusing for pppoe's case, in my opinion.

@c-po what do you think about it?