ospf6d: Release last dbdesc packet after router dead interval

ospf6d: Release last dbdesc packet after router dead interval

During the database description exchange process, the slave
releases the last dbdesc packet after router_dead_interval.
This was not implemented in the code.
I have written the function ospf6_neighbor_last_dbdesc_release,
which releases the last dbdesc packet after router_dead_interval.
This change was required as per the conformance test 13.11:

In state Full reception of a Database Description packet from
the master after this interval (RouterDeadInterval) will
generate a SeqNumberMismatch neighbor event.

Associated Parameters
  ICMPv6 Packet Listen Time
  ICMPv6 Packet Tolerance Factor
  ICMPv6 Packet Tolerance Time
  OSPFV3 DUT Interface Transmit Delay
  OSPF Reset Adjacencies Timeout
Test Actions
1.
2. 3.
ANVL: Establish full adjacency with DUT for neighbor Rtr-0-A on DIface-0, with DUT as slave.
ANVL: Wait (for <RouterDeadInterval> seconds).
ANVL: Send <OSPF-DD> packet from neighbor Rtr-0-A to DIface-0 con- taining:
• •
I-bit field not set M-bit field not set
MS-bit field set
DD sequence number same as the one last sent by ANVL.

. ANVL: Listen (for upto 2 * <RxmtInterval> seconds) on DIface-0.
5. DUT: Trigger the event SeqNumberMismatch and set the neighbor state for neighbor Rtr-0-A to ExStart.
6. DUT: Send <OSPF-DD> packet.
7. ANVL: Verify that the received <OSPF-DD> packet contains:
• I-bit field set
• M-bit field set
• MS-bit field set.

Test Reference
• RFC 5340, s4.2.1.2 p19 Sending Database Description Packets
  RFC 2328, s10.8 p104 Sending Database Description Packets.

Signed-off-by: Yash Ranjan <ranjany@vmware.com>
(cherry picked from commit bc09f3e6bbd9df931e259b16da4e7b7593d141c6)