net: yaip: Add ICMPv6 handler

The host will be able to respond to ICMPv6 messages.
An echo-request handler is implemented and it will send
echo-reply when needed.

Change-Id: I08f4703bab5cf3e95d3ae722ebc7a386d22fe17e
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>