ospfd: address CVE-2017-3224

ospfd: address CVE-2017-3224

Based on the vulnerability mentioned in 793496 an attacker can craft an
LSA with MaxSequence number wtih invalid links and not set age to MAX_AGE
so the lsa would not be flush from the database.

To address the issue, check incoming LSA is MaxSeq but Age is not set
to MAX_AGE 3600, discard the LSA from processing it.
Based on  RFC-2328 , When a LSA update sequence reaches MaxSequence
number, it should be prematurely aged out from the database with age set
to MAX_AGE (3600).

Ticket:CM-18989
Reviewed By:
Testing Done:

Signed-off-by: Chirag Shah <chirag@cumulusnetworks.com>