tipc: fix regression bug where node events are not being generated

Commit 5902385a ("tipc: obsolete
the remote management feature") introduces a regression where node
topology events are not being generated because the publication
that triggers this: {0, <z.c.n>, <z.c.n>} is no longer available.
This will break applications that rely on node events to discover
when nodes join/leave a cluster.

We fix this by advertising the node publication when TIPC enters
networking mode, and withdraws it upon shutdown.

Signed-off-by: Erik Hugne <erik.hugne@ericsson.com>
Reviewed-by: Jon Maloy <jon.maloy@ericsson.com>
Reviewed-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>