Augments TIPC's discovery object to track the number of neighboring nodes
having an active link to the associated bearer.

This means tipc_disc_update_link_req() becomes either one of:

       tipc_disc_add_dest()
or:
       tipc_disc_remove_dest()

depending on the code flow direction of things.
Signed-off-by: NAllan Stephens <Allan.Stephens@windriver.com>
Signed-off-by: NPaul Gortmaker <paul.gortmaker@windriver.com>