ospf6d : fix issue in ecmp inter area route

ospf6d : fix issue in ecmp inter area  route

Issue: When a path in the inter area ecmp route is deleted, the route is removed

Fix: The fix is to remove the specific path from the inter area route using
     ospf6_abr_old_route_remove() when abr route entry is not found.
     In  the function ospf6_abr_old_route_remove() the path to be removed needs
     to match adv router and link state ID

     Fixed memory leak in ospf6_intra_prefix_update_route_origin() caused by
     route node lock not getting released.

Signed-off-by: kssoman <somanks@gmail.com>