[PATCH 0/8 net-2.6.26] [NETNS]: namespace refcounting cleanup

Network namespace has two referrence counters:
- count
- use_count.
The namespace is scheduled to destruction automatically when the count
becomes 0.

There are several SLAB objects with a pointer to a namespace on them.
These objects are cleaned up during namespace stop. Some of them
increment use_count, some don't. This set fixes this discrepancy,
i.e. now all such objects increment the use_count.

Though, the use_count itself is used in a very debug manner and checked
only during namespace stop. So, I have placed it under
NETNS_REFCNT_DEBUG definition exactly like this is done for socket
refcounting code to remove extra atomic from any possible fast paths.

Signed-off-by: Denis V. Lunev <redacted>