ospf6d: Stitching the auth trailer code with rest of ospf6.

ospf6d: Stitching the auth trailer code with rest of ospf6.

Problem Statement:
==================
RFC 7166 support for OSPF6 in FRR code.

RCA:
====
This feature is newly supported in FRR

Fix:
====
Core functionality implemented in previous commit is
stitched with rest of ospf6 code as part of this commit.

Risk:
=====
Low risk

Tests Executed:
===============
Have executed the combination of commands.

Signed-off-by: Abhinay Ramesh <rabhinay@vmware.com>