Treat management network like another link

[ipspace]

Instead of handcrafting management IP addresses we should:

• Convert the management pool into a link-like data structure
• Use the "standard" interface address assignment logic to assign IPv4 or IPv6 addresses to management interfaces

This would allow management IP addresses specified as ints, address, or address/prefix. We would have to make an exception and reject True/False values though.

Based on https://github.com/ipspace/netlab/pull/1955#pullrequestreview-2632910371 by @jbemmel