[Feature](networking): remove checks for FIP networks for create router

[hgw77]

Description
Remove the checks for fip network and subnet in the create form for routers because these fields are optional from openstack side.

Problem Statement
The old behavior is to strict and was build in mind that the router is always used to communicate with the outside world. But routers can also be used to bind internal networks together. That was not possible with the old behavior because you must choose a FIP Network and subnet for the router.

Proposed Solution
Remove checks on controller and client side