[client] Use native windows sock opts to avoid routing loops (#4314)

- 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

client/internal/stdnet/dialer.go

@@ -5,7 +5,7 @@ import (
 
 	"github.com/pion/transport/v3"
 
-	nbnet "github.com/netbirdio/netbird/util/net"
+	nbnet "github.com/netbirdio/netbird/client/net"
 )
 
 // Dial connects to the address on the named network.

client/internal/stdnet/listener.go

@@ -6,7 +6,7 @@ import (
 
 	"github.com/pion/transport/v3"
 
-	nbnet "github.com/netbirdio/netbird/util/net"
+	nbnet "github.com/netbirdio/netbird/client/net"
 )
 
 // ListenPacket listens for incoming packets on the given network and address.