Adds new RawSocket class (and underlying jni implementation). This is a

utility class for an experimental Java implementation of dhcp.  The client
DHCP implementation needs to construct, send, receive, and parse raw L2
packets before the network interface is configured with an IP address.  Current
Java networking classes do not work with unconfigured network interfaces.

Change-Id: I4dd0133868da5b84bd2a471c33173d4c056c34e8