- Move `util/grpc` and `util/net` to `client` so `internal` packages can be accessed
- Add methods to return the next best interface after the NetBird interface.
- Use `IP_UNICAST_IF` sock opt to force the outgoing interface for the NetBird `net.Dialer` and `net.ListenerConfig` to avoid routing loops. The interface is picked by the new route lookup method.
- Some refactoring to avoid import cycles
- Old behavior is available through `NB_USE_LEGACY_ROUTING=true` env var
* Add Linux legacy routing if ip rule functionality is not available
* Ignore exclusion route errors if host has no route
* Exclude iOS from route manager
* Also retrieve IPv6 routes
* Ignore loopback addresses not being in the main table
* Ignore "not supported" errors on cleanup
* Fix regression in ListenUDP not using fwmarks
