ieee802154: add types for link-layer security

The added structures match 802.15.4-2011 link-layer security PIBs as
closely as is reasonable. Some lists required by the standard were
modeled as bitmaps (frame_types and command_frame_ids in *llsec_key,
802.15.4-2011 7.5/Table 61), since using lists for those seems a bit
excessive and not particularly useful. The DeviceDescriptorHandleList
was inverted and is here a per-device list, since operations on this
list are likely to have both a key and a device at hand, and per-device
lists of keys are shorter than per-key lists of devices.

Signed-off-by: Phoebe Buckheister <phoebe.buckheister@itwm.fraunhofer.de>
Signed-off-by: David S. Miller <davem@davemloft.net>