Linux legacy routing (#1774)

* 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

util/net/dialer.go

@@ -35,7 +35,7 @@ func DialUDP(network string, laddr, raddr *net.UDPAddr) (*net.UDPConn, error) {
 	udpConn, ok := conn.(*net.UDPConn)
 	if !ok {
 		if err := conn.Close(); err != nil {
-			log.Errorf("Failed to closeConn connection: %v", err)
+			log.Errorf("Failed to close connection: %v", err)
 		}
 		return nil, fmt.Errorf("expected UDP connection, got different type")
 	}

util/net/listener_generic.go

@@ -145,10 +145,19 @@ func closeConn(id ConnectionID, conn net.PacketConn) error {
 // ListenUDP listens on the network address and returns a transport.UDPConn
 // which includes support for write and close hooks.
 func ListenUDP(network string, laddr *net.UDPAddr) (*UDPConn, error) {
-	udpConn, err := net.ListenUDP(network, laddr)
+	conn, err := NewListener().ListenPacket(context.Background(), network, laddr.String())
 	if err != nil {
 		return nil, fmt.Errorf("listen UDP: %w", err)
 	}
-	connID := GenerateConnID()
-	return &UDPConn{UDPConn: udpConn, ID: connID, seenAddrs: &sync.Map{}}, nil
+
+	packetConn := conn.(*PacketConn)
+	udpConn, ok := packetConn.PacketConn.(*net.UDPConn)
+	if !ok {
+		if err := packetConn.Close(); err != nil {
+			log.Errorf("Failed to close connection: %v", err)
+		}
+		return nil, fmt.Errorf("expected UDPConn, got different type")
+	}
+
+	return &UDPConn{UDPConn: udpConn, ID: packetConn.ID, seenAddrs: &sync.Map{}}, nil
 }