Use MulticastLock

[pocmo]

Even though I successfully sent and received multicast packets between Nexus devices (Galaxy Nexus, Nexus 7, Nexus 10) the Wifi stack of a device might filter these packets. Therefore we need to acquire a MulticastLock from the WifiManager.

Allows an application to receive Wifi Multicast packets. Normally the Wifi
stack filters out packets not explicitly addressed to this device. Acquring
a MulticastLock will cause the stack to receive packets addressed to
multicast addresses. Processing these extra packets can cause a
noticable battery drain and should be disabled when not needed.

https://developer.android.com/reference/android/net/wifi/WifiManager.MulticastLock.html