Add build ICMPv6 echo request packet helper function in Ipv6Utils. am: 657b2e8660 am: 21839bcbdd

Original change: https://android-review.googlesource.com/c/platform/frameworks/libs/net/+/1669829

Change-Id: I74e2fab9a47dc0daf4d9a6ae8f406aecc6160eab