nixos/network-interfaces: IPs must always be set

Previously, depending on the environment and the type of interface that
was created, the configured IPs of an interface wouldn't be applied on a
nixos-rebuild switch. It works after a reboot.

This patch ensures that the network-addresses service is started
either via the network-link service or if the networking target is
activated (i.e. on system activation).

Fixes #28474 #16230.