ieee802.15.4 loopback:  Better simulation addressing: sort, extended, panid, and IP address conversion

clicker2-stm32: mrf24j40-6lowpan configuration needs to enabled the ieee 802.15.4 MAC network device as well.

Clicker2-STM32:  Enable networking and 6loWPAN in the mrf24j40-6lowpan configuration.  Fix a couple of new 6loWPAN compile issues revealed by this new configuration.

STM32 SPI/I2S:  Back out a bad pin mapping change from 4ab2a366.  Try to staighten out some I2C3 and SPI3 pin configuration stuff.

STM32 F4 FLASH:  Enable/disable the flash write protection on any sector.  I have verified it to work on the stm32f427.

samv7:twihs driver add reference counting

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

wireless/ieee802154: Fixes issue with wrong information being sent in a rejected association response frame

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

wireless/ieee802154: Fixes issue with wrong information being sent in a rejected association response frame

wireless/ieee802154: Lots of fixes, cleanup, new functionality.  Functional

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

configs/.gitignore:  Make sure that any .gdbinit, .project, or .cproject files are ignore so that they are less likely to be included in a patch or PR.

Update tools/configure.c to same functionality as configure.sh.  Add an array of optional file names.  Currently, .gdbinit is the only optional file but other things like IDE-specific project files might need to be copied as well.

Improve configure.sh behavior (proposal).

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

 - enable to call from top directory.
 - enable to designate direct path for config.
 - install .gdbinit if the target has.

Fixed typo "CORTEXR5F" in arch/arm/Kconfig

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

Fixed ARMv7-M Toolchain definition for Cortex-M4.

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

 - Cortex-M4 only have Single Precision FPU.