If ip6 but no gw6 is provided, fall back to ra

[JanGerritsen]

Current behavior and problem:
IPv6 router advertisements are only evaluated, if the PVE configuration is set to SLAAC. It is not possible to set a fixed (static) IPv6 address, but let the system discover the address of the router.

Change:
Since the gateway address is already optional, this patch changes the following:
If a static IPv6 address is specified, but no gateway address is given, enable router discovery via router advertisement.
If both are specified, router advertisement stays disabled.

PS: This is my first patch to this project. I couldn’t find a contributor documentation, so I am not sure what your procedure for patches is. Please let me know if you need additional input.

PPS:
Since the indentation of the original code was off, I have tried to match it as good as possible.

[ThomasLamprecht]

Hello! Thanks for your contribution, but we do not use GitHub for our workflow, the repos here are a read-only mirror to avoid name-squatting (happened in the past).

Please see our wiki for how to contribute:
https://pve.proxmox.com/wiki/Developer_Documentation

Note also the CLA requirement (see at the bottom).

The general intent of your patch seems alright, but I did not look into it all too closely.

W.r.t. to your code-changes some comments upfront:

• the indentation is wrong, we curretnly still use a 4 level indentation with every two full level been collapsed into a tab:
  https://pve.proxmox.com/wiki/Perl_Style_Guide
• the $gw variable is unused
  You could simply use a post-if here:

$accept_ra = 'true' if !defined($d->{gw6});

or keep the "full-blown" if, but drop the my $gw = part if it's not used anyway.

[deviantintegral]

I filed a feature request similar to this at https://bugzilla.proxmox.com/show_bug.cgi?id=5538.