An interop test of Authenticated Header (AH) using sha2_256 to ensure there
is no trunc bug issue.

This uses IKEv2. It requires xfrm

This test requires strongswan 5.1.1 or newer for AH support.

As of strongswan-5.5.2 is performs AH alignment differently, and the kernel
doesn't support either alignment. Requires an update to libreswan
