feat: Support multiple bind addresses for dual-stack (IPv4 + IPv6)

[jakobve]

What is this PR about and why is it needed?

• The current ha_proxy.binding_ip property accepts a single scalar address. Combined with ha_proxy.v4v6: true, it enables dual-stack by creating one IPv6 socket that also accepts IPv4 connections via the kernel's IPv4-mapped IPv6 mechanism (::ffff:x.x.x.x).
• When setting binding_ip: :: ONLY IPv6 traffic will be accepted by setting the v6only flag explicitly.
  • When dual stack is wanted one needs to set v4v6: true
  • When wanting IPv6 only v4v6 has to be false or empty
• When setting multiple binding_ips and one of them is an IPv6 address the v6only flag is set explicitly
• binding_ips cannot be combined with v4v6. The v4v6 property has to be empty. Cannot be set to false

Additional notes for reviewers

+++ This is can be a breaking change +++
When binding_ip is set to :: and the v4v6 flag is not set or false only accept IPv6 traffic by setting the v6only flag.

Which issues does this fix?

#983

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: jakobve / name: Jakob Bergmeier (0014d2d, 4a24ca4, 791e3bf, 7c1d716, 884a00b, bbbd406, dc3e3ef)