ospf6d: Added changes to track route-map usage

ospf6d: Added changes to track route-map usage

Made changes and updated the routemap applied
counter in the following flows.
1.Increment the routemap applied counter when route map
  attached to a redistribution list.
  The counter will be updated if the routemap exists.
2.Decrement when route map removed / modified from a
  redistribution  list.
3.Increment/decrement when route map create/delete
  callback triggered.

Signed-off-by: RajeshGirada <rgirada@vmware.com>