tipc: purge deferred updates from dead nodes

If a peer node becomes unavailable, in addition to removing the
nametable entries from this node we also need to purge all deferred
updates associated with this node.

Signed-off-by: Erik Hugne <erik.hugne@gmail.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>