This patch fixes and simplifies locking in the SELiunux netif cache.

An old problem (which I forgot about) is fixed where a netif lookup can be
followed by a preemption, causing a race against sel_netif_put().  Kaigai
Kohei discovered a problem where netif lookups were also not protected
against races with sel_netif_flush().

The code has now been reworked to fix these problems, eliminate the
refcounting and remove atomic operations entirely from the read path
(generally making better use of RCU).  The avc entry ref has been removed
as part of this simplification in anticipation of an RCU scalability patch
which removes them in general.
Signed-off-by: James Morris <jmorris@redhat.com>
Signed-off-by: Stephen Smalley <sds@epoch.ncsc.mil>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>