Networking: Modify event list handling:  Now there are two event lists each device structure:  (1) One is for ARP and ICMP data related evetns, the other is for device related events.  Callback allocation/free routines no accept a device paramter as well as a list: If the device paramter is added, then the callback goes into both the connection-related liast AND the device event list.  Thus each socket type can received both custom data-related events as well as common device related events.

Networking:  Fixes an important TCP bug: 16-bit flags was being converted to 8-bits in a few locations, causing loss of status indications

Networking:  No that ARP, ICMP, and ICMPv6 reside in the same list we need to make the definitions of ARP_POLL, ICMP_POLL, and ICMPv6_POLL different because there are small differences in the context for each.

Extend device specific callbacks to ICMPv6 and ARP.  Fix some IPv6 compilation errors that have crept in

Basic support for the Kinetis K20 architecture.  Taken from PX4.  This is the work of Jakob Odersky.

SAML21-Xlplained: Add options to enable XOSC32K and to use it as the DFLL source; NSH configure now uses DFLL with OSC16M source

Logic that samples the free running counter reads the pending interrupt status regsiter and can cause interrupts to be lost.  So, if when the status regsiter is read, the logic must also handle the timer overflow event.  Found and fixed by Max Neklyudov

All minnsh configurations: Removing CONFIG_ARCH_STACKDUMP we reduce more 424 bytes.  Alan Carvalho de Assis