Use new mutex API
Check if source address is not illegal source address.

Check if source address is not multicast or unique local unicast (for
non-local destinations.

Fixes issue #78
Don't note address operators as bit-wise and.

Fix https://github.com/authmillenon/RIOT/blob/3fddddd3be31a26684b21b1580f38c34cf2af81e/sys/net/rpl/rpl.c#L75