tipc: update cluster capabilities if node deleted

There are two improvements when re-calculate cluster capabilities:

- When deleting a specific down node, need to re-calculate.
- In tipc_node_cleanup(), do not need to re-calculate if node
is still existing in cluster.

Acked-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: Hoang Le <hoang.h.le@dektech.com.au>
Acked-by: Jon
Signed-off-by: David S. Miller <davem@davemloft.net>