ospf6d: "clear ipv6 ospf6 process" command

ospf6d: "clear ipv6 ospf6 process" command

Adding the "clear ipv6 ospf6 command" . It resets
the ospfv3 datastructures and clears the database
as well as route tables. It resets the neighborship
by restarting the interface state machine.
If the user wants to change the router-id, this
command updates the router-id to the latest static
router-id and starts the neighbor formation with
the new router-id.

Signed-off-by: Yash Ranjan <ranjany@vmware.com>