ospf6d: minor struct compare issues.

ospf6d: minor struct compare issues.

Problem Statement:
Multiple struct compare using memcmp, which might result in issue due to
structure padding/alignment.

Fix:
The code changes involve structure member by member comparison to
remove any issues related to padding/alignment.

Signed-off-by: Manoj Naragund <mnaragund@vmware.com>
(cherry picked from commit 67db821a1d6d68b19862d50b68ed19278c5f2422)