Review MulticastLock usage on Android hello sample

[pepone]

According to the doc this is required to allow application to receive multicast packages. We acquire it upon starts and never release it.

I think this might be only required when IceDiscovery is enabled in the sample application, and it would be better to acquire/release it when IceDiscovery is enabled/disabled.

ice-demos/java/android/hello/src/main/java/com/zeroc/hello/HelloApp.java

Lines 81 to 82 in 2fae807

	WifiManager.MulticastLock lock = wifiManager.createMulticastLock("com.zeroc.hello");
	lock.acquire();