network: make address_get() work for null address

network: make address_get() work for null address

When a static null address is requested, e.g. Address=0.0.0.0/24,
then the corresponding Address object owned by Network object has
null address, and previously it did not match any addresses already
assigne to the interface.

Let's search matching Address object when originally it is requested as
the null address.

Then, the address configured with requested as a null address will be
kept on reconfigure.

Fixes #26113.