net: network drver now retains Ethernet MAC address in a union so that other link layer addresses may be used in a MULTILINK environment.

6loWPAN: Remove the PAN ID from the 6loWPAN data structure.  This is owned by the radio driver.  Rather, use an IOCTL to obtain the PAN ID from the downstream radio driver.

Some trivial spacing changes from review of last PR; Remove some dangling whitespace at the end of lines.

wireless/ieee802154: Simplifies TX completion interface.  Documents and cleans up some functions

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

wireless/ieee802154: Work on packet reception at radio layer (MRF24J40)

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

clock: Add new type ssystime_t for relative 64-bit ticks, change ticks<->time conversion functions to use ssystime_t

Add clock_resynchronize for better synchronization of CLOCK_REALTIME and CLOCK_MONOTONIC to match RTC after resume from low-power state.

Add up_rtc_getdatetime_with_subseconds under CONFIG_ARCH_HAVE_RTC_SUBSECONDS to allow initializing (and resynchronizing) system clock with subseconds accuracy RTC.

Move net/iob to drivers/iob so that the I/O buffering feature can be available to other drivers when networking is disabled.

procfs: Fix wrong member IDs are displayed when 'cat /proc/<pid>/group/stasus'.

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