network: use request queue to configure addresses, routes, and nexthops

network: use request queue to configure addresses, routes, and nexthops

Why is this necessary? Several examples below.

- When a route sets prefsrc, then the address must be already assigned
  (see issue #19285), and also it must be ready if IPv6.
- When a route or nexthop sets gateway, then the address must be reachable.
- When a route sets nexthop ID, then the corresponding nexthop must be
  assigned.
- When a route sets multipath routes on another interface, then the
  interface must exist and be ready to configure.
- When configuring address, the same address must not be under removing
  (see issue #18108).
Etc,. etc,...

So, this makes all requests about addresses, routes, and nethops are once
stored in the queue, and will be processed when they are ready to configure.

Fixes #18108 and #19285.