tipc: withdraw tipc topology server name when namespace is deleted

The TIPC topology server is a per namespace service associated with the
tipc name {1, 1}. When a namespace is deleted, that name must be withdrawn
before we call sk_release_kernel because the kernel socket release is
done in init_net and trying to withdraw a TIPC name published in another
namespace will fail with an error as:

[  170.093264] Unable to remove local publication
[  170.093264] (type=1, lower=1, ref=2184244004, key=2184244005)

We fix this by breaking the association between the topology server name
and socket before calling sk_release_kernel.

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