ospf6d: Core functionality of auth trailer implementation..

ospf6d: Core functionality of auth trailer implementation..

Problem Statement:
==================
Implement RFC 7166 support for OSPF6 in FRR code.

RCA:
====
This feature is newly supported in FRR.

Fix:
====
Changes are done to implement ospf6 ingress and egress
packet processing.
This commit has the core functionality.

It supports below debugability commands:
---------------------------------------
debug ospf6 authentication [<tx|rx>]

It supports below clear command:
--------------------------------
clear ipv6 ospf6 auth-counters interface [IFNAME]

It supports below show commands:
--------------------------------
frr# show ipv6 ospf6 interface ens192
ens192 is up, type BROADCAST
  Interface ID: 5
  Number of I/F scoped LSAs is 2
    0 Pending LSAs for LSUpdate in Time 00:00:00 [thread off]
    0 Pending LSAs for LSAck in Time 00:00:00 [thread off]
  Authentication trailer is enabled with manual key         ==> new info added
    Packet drop Tx 0, Packet drop Rx 0			    ==> drop counters

frr# show ipv6 ospf6 neighbor 2.2.2.2 detail
 Neighbor 2.2.2.2%ens192
    Area 1 via interface ens192 (ifindex 3)
    0 Pending LSAs for LSUpdate in Time 00:00:00 [thread off]
    0 Pending LSAs for LSAck in Time 00:00:00 [thread off]
    Authentication header present                           ==> new info added
                         hello        DBDesc       LSReq        LSUpd        LSAck
      Higher sequence no 0x0          0x0          0x0          0x0          0x0
      Lower sequence no  0x242E       0x1DC4       0x1DC3       0x23CC       0x1DDA

frr# show ipv6 ospf6
 OSPFv3 Routing Process (0) with Router-ID 2.2.2.2
 Number of areas in this router is 1
 Authentication Sequence number info                       ==> new info added
  Higher sequence no 3, Lower sequence no 1656

Risk:
=====
Low risk

Tests Executed:
===============
Have executed the combination of commands.

Signed-off-by: Abhinay Ramesh <rabhinay@vmware.com>