Squashed commit of the following:

commit 7029dffd02156bcbfa84262671c2ca766a117191
Author: Gregory Nutt <gnutt@nuttx.org>
Date:   Sat Jul 29 12:02:13 2017 -0600

    6LoWPAN PktRadio: Add missing MetaData-related prototypes and initialization logic.  Perform a major renaming to make room in the 6LoWPAN name space for packet radios.

commit e2012f7c1df14155c0bfd45d7f1cb3f71b259f48
Author: Gregory Nutt <gnutt@nuttx.org>
Date:   Sat Jul 29 10:16:23 2017 -0600

    6LoWPAN PktRadio:  Some initial changes to support raw packet radios without IEEE 802.15.4 with 6LoWPAN.

commit c6dbf9178539b7da75e492ffd1d1f93c9c326299
Merge: da782d6cdf 5889ce65
Author: Gregory Nutt <gnutt@nuttx.org>
Date:   Sat Jul 29 07:30:08 2017 -0600

    Merge remote-tracking branch 'origin/master' into spirit

commit da782d6cdff5980d71aaa2da5f9c28ab3438d085
Author: Gregory Nutt <gnutt@nuttx.org>
Date:   Sat Jul 29 07:26:48 2017 -0600

    Spirit:  Completes port of the spirit radio library to NuttX.

commit 63f3595c47dca13952d28b518c7f0a...