net, atm: convert lec_arp_table.usage from atomic_t to refcount_t

refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/atm/lec_arpc.h

@@ -47,7 +47,7 @@ struct lec_arp_table {
 					 * the length of the tlvs array
 					 */
 	struct sk_buff_head tx_wait;	/* wait queue for outgoing packets */
-	atomic_t usage;			/* usage count */
+	refcount_t usage;		/* usage count */
 };
 
 /*