Implement UDP multicast handler start/stop to ensure proper lifecycle (#9524)

* Implement UDP multicast handler start/stop to ensure proper lifecycle

* Add close method to AsyncUDP and improve UDP multicast handler lifecycle management

* Guard portduino

src/platform/nrf52/AsyncUDP.cpp

@@ -36,6 +36,13 @@ bool AsyncUDP::writeTo(const uint8_t *data, size_t len, IPAddress ip, uint16_t p
     return udp.endPacket();
 }
 
+void AsyncUDP::close()
+{
+    udp.stop();
+    localPort = 0;
+    _onPacket = nullptr;
+}
+
 // AsyncUDPPacket
 AsyncUDPPacket::AsyncUDPPacket(EthernetUDP &source) : _udp(source), _remoteIP(source.remoteIP()), _remotePort(source.remotePort())
 {

src/platform/nrf52/AsyncUDP.h

@@ -22,6 +22,7 @@ class AsyncUDP : public Print, private concurrency::OSThread
 
     bool listenMulticast(IPAddress multicastIP, uint16_t port, uint8_t ttl = 64);
     bool writeTo(const uint8_t *data, size_t len, IPAddress ip, uint16_t port);
+    void close();
 
     size_t write(uint8_t b) override;
     size_t write(const uint8_t *data, size_t len) override;