[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

sharedsock/sock_linux.go

@@ -22,7 +22,7 @@ import (
 	"golang.org/x/sync/errgroup"
 	"golang.org/x/sys/unix"
 
-	nbnet "github.com/netbirdio/netbird/util/net"
+	nbnet "github.com/netbirdio/netbird/client/net"
 )
 
 // ErrSharedSockStopped indicates that shared socket has been stopped
@@ -93,7 +93,7 @@ func Listen(port int, filter BPFFilter, mtu uint16) (_ net.PacketConn, err error
 	}
 
 	if err = nbnet.SetSocketMark(rawSock.conn4); err != nil {
-		return nil, fmt.Errorf("failed to set SO_MARK on ipv4 socket: %w", err)
+		return nil, fmt.Errorf("set SO_MARK on ipv4 socket: %w", err)
 	}
 
 	var sockErr error
@@ -102,7 +102,7 @@ func Listen(port int, filter BPFFilter, mtu uint16) (_ net.PacketConn, err error
 		log.Errorf("Failed to create ipv6 raw socket: %v", err)
 	} else {
 		if err = nbnet.SetSocketMark(rawSock.conn6); err != nil {
-			return nil, fmt.Errorf("failed to set SO_MARK on ipv6 socket: %w", err)
+			return nil, fmt.Errorf("set SO_MARK on ipv6 socket: %w", err)
 		}
 	}