ospfd: Fix RFC conformance test cases 25.19 and 27.6

ospfd: Fix RFC conformance test cases 25.19 and 27.6

Steps to reproduce:
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1. ANVL: Establish full adjacency with DUT for neighbor Rtr-0-A on DIface-0 with DUT as DR.
2. ANVL: Listen (for up to 2 * <RxmtInterval> seconds) on DIface-0.
3. DUT: Send <OSPF-LSU> packet.
4. ANVL: Verify that the received <OSPF-LSU> packet contains a Network- LSA for network N1
   originated by DUT, and the LS Sequence Number is set to <InitialSequenceNumber>.
5. ANVL: Establish full adjacency with DUT for neighbor Rtr-0-B on DIface-0 with DUT as DR.
6. ANVL: Listen (for up to 2 * <RxmtInterval> seconds) on DIface-0.
7. DUT: Send <OSPF-LSU> packet.
8. ANVL: Verify that the received <OSPF-LSU> packet contains a new instance of the
   Network-LSA for network N1 originated by DUT, and the LS Sequence Number
   is set to (<InitialSequenceNumber> + 1).

Both the test cases were failing while verifying the initial sequence number for network LSA.

This is because currently OSPF does not reset its LSA sequence number when it is going down.

Signed-off-by: Mobashshera Rasool <mrasool@vmware.com>
(cherry picked from commit ca5997cd018ec66534285130d02de168a3a4ed5c)