CC2420: Added RSSI_OFFSET as described in the manual
CC2420: Simplified prepare
Sky: Use the cc2420_aes_128_driver by default
ContikiMAC: Create and parse ContikiMAC header in special framer; Expanded framer interface
to allow for creating and securing frames in advance; Create and secure frames in advance when sending bursts; Do neither recreate nor resecure frames that come from phase
sicslowpan: Fixed too aggresive fragmentation