Transport: Bind the UDP outbound socket in the destination family (#6688)

https://github.com/XTLS/Xray-core/pull/6688#issuecomment-5445559197

Completes https://github.com/XTLS/Xray-core/pull/6624#issuecomment-5430488664

---------

Co-authored-by: 风扇滑翔翼 <Fangliding.fshxy@outlook.com>

transport/internet/system_dialer.go

@@ -50,18 +50,24 @@ func (d *DefaultSystemDialer) Dial(ctx context.Context, src net.Address, dest ne
 	errors.LogDebug(ctx, "dialing to "+dest.String())
 
 	if dest.Network == net.Network_UDP {
-		srcAddr := resolveSrcAddr(net.Network_UDP, src)
-		if srcAddr == nil {
-			srcAddr = &net.UDPAddr{
-				IP:   []byte{0, 0, 0, 0},
-				Port: 0,
-			}
-		}
-		var lc net.ListenConfig
 		destAddr, err := net.ResolveUDPAddr("udp", dest.NetAddr())
 		if err != nil {
 			return nil, err
 		}
+		srcAddr := resolveSrcAddr(net.Network_UDP, src)
+		if srcAddr == nil {
+			// some OS don't support mapped IPv4 dual stack
+			// and need to select 0.0.0.0 or [::] manually based on the destination
+			wildcard := net.AnyIP.IP()
+			if destAddr.IP.To4() == nil {
+				wildcard = net.AnyIPv6.IP()
+			}
+			srcAddr = &net.UDPAddr{
+				IP:   wildcard,
+				Port: 0,
+			}
+		}
+		var lc net.ListenConfig
 		lc.Control = func(network, address string, c syscall.RawConn) error {
 			for _, ctl := range Controllers {
 				if err := ctl(network, address, c); err != nil {