Ieee802154

Approved-by: Gregory Nutt <gnutt@nuttx.org>

6loWPAN:  Add some checks for the case where there are multiple network devices and multiple link layer protocols.

not a clean fix, but at least makes DHCP working with CONFIG_NETDEV_MULTINIC

Approved-by: Gregory Nutt <gnutt@nuttx.org>

Revert "Add a placeholder for nucleo-64 boards.  Currently these are in various directories nucleo-f303re, nucleo-f334r8, and nucleo-l476rg but need to be consolidated here because these are all the same boards."

This reverts commit 935cc4e3.

Add a placeholder for nucleo-64 boards.  Currently these are in various directories nucleo-f303re, nucleo-f334r8, and nucleo-l476rg but need to be consolidated here because these are all the same boards.

ieee802.15.4: New global functions exported by the lower MAC layer should be private to the MAC module.  Function prototypes moved from include/nuttx/wireless/ieee802154/ieee802154_mac.h to wireless/ieee802154/mac802154.h

IEEE802.15.4:  There is only one instance of the IEEE802.15.4 MAC lower level.  There is no need for the interface to be indirect via a vtable.  In this case, standard global functions should be used.