This comment adds (1) basic support for AF_BLUETOOTH sockets.  The logic compiles but is still incomplete.  Support for Bluetooth is general is still dependent on CONFIG_EXPERMIMENTAL because it is not yet ready for used.

Squashed commit of the following:

    wireless/bluetooth:  Some small changes that gets to a clean compile by just eliminating some incorrect implementations (still with a lot of warnings.  The logic is still incomplete but now not so lethal.
    wireless/bluetooth:  Restructuring:  Connection interfaces should internal to wireless/bluetooth.  include/nuttx/wireless/bt_conn.h removed and merged with wireless/bluetooth/bt_conn.h.  Several fix to get closer to bt_netdev.c compiling.  Need to design some not interfaces and use some existing interfaces to send and receiv packets.
    wireless/bluetooth: Some organization with some network device compile errors fixed.  Still not even close to compiling.
    net/bluetooth:  Fix numerous compile issues; Still open design issues with regard to the interface with the Bluetooth stack.
    wireless/bluetooth:  Create bt_netdev.c with a crude copy of mac802154_netdev.c.  Does not not even compile yet.
    include/nuttx/net:  Add bluetooth.h.  Content is not yet correct.
    net/netpackets:  Add bluetooth.h.  Update net/bluetooth to use new socket address definition.
    net/bluetooth:  Some fixes for initial build.
    net/bluetooth:  Add initial support for Bluetooth sockets.  The initial cut is just the a clone of the IEEE 802.15.4 socket support with name changes.
    net/ieee802154:  Fix some typos noted when cloning to create net/bluetooth.

6LoWPAN/Radio:  Rename radio property sp_pktlen to sp_framelen.  Add 6LoWPAN utility to get the max frame length (not yet hooked in)

6LoWPAN:  The original, Contiki-based design used only a single buffer for reassemblying larger packets.  This could be a problem issue for hub configurations which really need the capability concurrently reassemble multiple incoming streams concurrently.  These was also a design issue in that the reassembly buffer could be corrupted by outgoing packets.  The design was extended to support multiple reassembly buffers, each associated with the reassembly tag and source address.  This assures that there can be be no corruption of the reassembly once it has started.

6LoWPAN/PF_IEEE802154:  Created radiodev.h and renamed various structures to provide a better separation between 6LoWPAN and PF_IEEE802154.