ospf6d: Enable the feature using configure.ac

ospf6d: Enable the feature using configure.ac

Problem Statement:
=================
The feature is not enabled, needs to be enabled by doing required
initialization.

RCA:
====
Changes to support the feature is present, but the feature macro
needs to be enabled.

Fix:
====
This commit has changes to enable the code.

Risk:
=====
Medium

Need to ensure all existing ospf6 related topotests pass. to ensure
packet processing is not impacted.

Tests Executed:
===============
Have tested the functionality with enabling openssl and also disabling
openssl.

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