Add UDP multicast support on linux.

We tested it an it works.

This is really hacky to say the least.

arch/portduino/portduino.ini

@@ -1,6 +1,6 @@
 ; The Portduino based 'native' environment. Currently supported on Linux targets with real LoRa hardware (or simulated).
 [portduino_base]
-platform = https://github.com/meshtastic/platform-native.git#562d189828f09fbf4c4093b3c0104bae9d8e9ff9
+platform = symlink://../platform-native
 framework = arduino
 
 build_src_filter = 
@@ -34,10 +34,12 @@ build_flags =
   -Isrc/platform/portduino
   -DRADIOLIB_EEPROM_UNSUPPORTED
   -DPORTDUINO_LINUX_HARDWARE
+  -DHAS_UDP_MULTICAST
   -lpthread
   -lstdc++fs
   -lbluetooth
   -lgpiod
   -lyaml-cpp
   -li2c
+  -luv
   -std=c++17