Fix UDP Socket Binding Issue on Linux for IPv4 and IPv6

On Linux, when using UDP sockets, both IPv6 and IPv4 addresses are
bound to the same socket by default. This can cause issues when
sending and receiving packets across different address families.
Specifically, if we receive a packet from an IPv4 address,
attempting to send a response using an IPv6 address fails.

net/connUDP.go

@@ -57,6 +57,13 @@ func (c *ControlMessage) GetIfIndex() int {
 	return c.IfIndex
 }
 
+func (c *ControlMessage) GetDst() net.IP {
+	if c == nil {
+		return nil
+	}
+	return c.Dst
+}
+
 type packetConn interface {
 	SetWriteDeadline(t time.Time) error
 	WriteTo(b []byte, cm *ControlMessage, dst net.Addr) (n int, err error)
@@ -516,6 +523,13 @@ func (c *UDPConn) writeTo(raddr *net.UDPAddr, cm *ControlMessage, buffer []byte)
 		// because the connection is already established.
 		return c.connection.Write(buffer)
 	}
+	// On Linux, UDP network binds both IPv6 and IPv4 addresses to the same socket.
+	// When receiving a packet from an IPv4 address, we cannot send a packet from an IPv6 address.
+	// Therefore, we wrap the connection using an IPv4 packet connection (packetConn).
+	if !IsIPv6(raddr.IP) && c.packetConn.IsIPv6() {
+		pc := packetConnIPv4{packetConn: ipv4.NewPacketConn(c.connection)}
+		return pc.WriteTo(buffer, cm, raddr)
+	}
 	return c.packetConn.WriteTo(buffer, cm, raddr)
 }