ospfd: OSPF opaque LSA stale processing fix and topotests.

    ospfd: OSPF opaque LSA stale processing fix and topotests.

        1. Fix OSPF opaque LSA processing to preserve the stale opaque
            LSAs in the Link State Database for 60 seconds consistent with
            what is done for other LSA types.
         2. Add a topotest that tests for cases where ospfd is restarted
            and a stale OSPF opaque LSA exists in the OSPF routing domain
            both when the LSA is purged and when the LSA is reoriginagted
            with a more recent instance.

Signed-off-by: Acee <aceelindem@gmail.com>