sockettest: Check for IPv4-in-IPv6 parsing and formatting
sockettest: Check for IPv4-in-IPv6 parsing and formatting

There are two standards how IPv4 address in IPv6 can be
expressed:

  ::10.1.2.3
  ::ffff:10.1.2.3

The former is obsolete and the latter should be used instead [1].
Add test cases to our sockettest to exercise parsing/formatting
of the valid address format.

1: https://datatracker.ietf.org/doc/html/rfc4291#section-2.5.5.1

Signed-off-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>
Reviewed-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>

libvirt/libvirt,crobinso/libvirt,zippy2/libvirt,libvirt/libvirt,libvirt/libvirt,olafhering/libvirt,olafhering/libvirt,libvirt/libvirt,zippy2/libvirt,crobinso/libvirt,olafhering/libvirt,olafhering/libvirt,zippy2/libvirt,jfehlig/libvirt,jfehlig/libvirt,jfehlig/libvirt,crobinso/libvirt,crobinso/libvirt,jfehlig/libvirt,zippy2/libvirt