removing possible invalid check

Checking for a link local address to determine if a node is on-link is
probably not a valid assumption in most wireless networks.
Added standard way to query CCA status on CC2420 transceiver (squashed)
Completed CC2420 constants documentation (DOxygen)
Fixed error caused by non-inclusion of cc2420_txrx() prototype
Fixed implementation of channel_clear() function
Change year of file copyright
Fix for WSN430 1.4 driver
Merge pull request #873 from OlegHahm/on_link_check

net: sixlowpan: removing possible invalid check
Fix length of fragmentation buffer in 6LoWPAN
Merge pull request #870 from authmillenon/fragbuf

sys:net:sixlowpan: Fix length of fragmentation buffer in 6LoWPAN
Merge pull request #915 from rousselk/radio-cca

Add a standard way to query CCA status on CC2420 transceiver.