STM32: Add an IPv6 configuration for the STM32F4-Discovery board (witht he STM32-DISCO_BB base board).  Verify that the STM32 Ethernet driver works with IPv6.

Networking:  Add support for sending ICMPv6 Router Solicitation and receiving Router advertisement.  This is a part of the ICMPv6 auto-configuration logic is still still not complete

Auto neighbor solicitation is no longer EXPERIMENTAL and is the default for the DK-TM4C129X/ipv6 configuration

ICMPv6: Adds basic logic to support verification that we have the IPv6 address in the Neighbor Table.  This feature is important because otherwise the first packet sent to a remote peer will fail (it will be replaced with a Neighbor Solicitation).

drivers/ramdisk.c and include/nuttx/fs/ramdisk.h:  Add logic to dispose of the drvier and RAM buffer when the RAM disk has been unlinked and all open references to the RAM disk have been closed.  Add new parameters to romdisk() to specify what should be done with the RAM/ROM buffer -- Should it be freed or not?  Changed all calls to ramdisk() to use these new parameters.

Moteino Mega:  Rename files to conform to newer standards.  Need to fix all of the old configurations someday

Get USART 2 & 3 working on lpc4357-evb. These changes are required to get USART 2 and 3 working on the Embest development board.  From Toby Duckworth

First step at porting to MoteinoMEGA.  LED shows assert failure at boot.  Appears to be short double blink, short off (~1sec), followed by 250ms toggle cycles.  Most of it derived from amber board.

Remove CONFIG_DEBUG_STACK.  Adding CONFIG_STACK_COLORATION makes this configuration option pointless