Fix problems in last commit noted by Jeongchan Kim:  last change returned -EINVAL vs EINVAL; Treat the case where the mutex is already unlocked just like the case where the mutex is held by another thread -- return EPERM.

6LoWPAN: Correct a few addressing issues.  The apps/examples/udp test now appears to be fully functional.  Also reserve two bytes at the end of the frame for the FCS.

wireless/ieee802154: Minor naming change to align better with coding guidelines

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

Make naming of NTXDESC consistent.  I don't know where it should be MAC or IEEE, gut I changed the one that affects the fewest files.

pthread_mutex_unlock():  Missing check for the case where pthread_mutex_lock() is called when the mutex is not locked.  In that case, it would increment the underlying semaphore avove 1.  This is the fix for a problem noted by initialkjc@yahoo.com.

ieee802154 MAC: Free allocated TX descriptor if an error occurs after the descriptor has been allocated.

ieee802154_req_data:  Don't modify the IOB until we are certain that no EINTR errors will occur.  Otherwise, the retry will fail

Kinetis:I2C fixed mis-placed kinetis_i2c_endwait

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

   Fixed accedently replaced post with wait.

Kinetis:I2C driver added I2C3, reference counting and reset

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

ieee802154 network driver now retries if ieee802154_req_data() returns EINTR.  In clicker2-stm32 6LoWPAN configuration, increased the number of TX descriptors to match then number of IOBs.

   Refactored the driver to support reference counting and reset
   added I2C3

STM32:  Allow clock frequencies > 168 Mhz on stm32f427/429.  We need to enable the power overdrive for this case.  This patch allows the required bits to be set in proper sequence.  It also modifies the local register access operations to allow more than 16-bit registers.

6LoWPAN: Add debug statements; Update configuration, need to specific 6LoWPAN compatible port numbers.