Add a test for IP_MULTICAST_ALL for DatagramSocket

This option defaults to 1 for AF_INET dgram sockets and 0 for AF_INET6.
Android uses AF_INET6 sockets and don't need to explicitly set the
option, but it is better to have a test to assert this behaviour.

Test: org.apache.harmony.tests.java.net.DatagramSocketTest
Change-Id: I367be7f2a1bc7fd4836a132f16ecfd3ca65b930a