Implement ICMPv6 echo request packet filter.

This commit implements a filter to identify ICMPv6 echo request packets.
If the request is directed to the host, the packet is passed. This lays
the groundwork for implementing ICMPv6 echo request offload.

Test: TH
Change-Id: Ie0d3ec1c78fa38bd1d9a53e8c698aff848df2b91
5 files changed