[NET]: sparse warning fixes

Fix a bunch of sparse warnings. Mostly about 0 used as
NULL pointer, and shadowed variable declarations.
One notable case was that hash size should have been unsigned.

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/atm/signaling.c

@@ -230,7 +230,7 @@ static void sigd_close(struct atm_vcc *vcc)
 		struct hlist_head *head = &vcc_hash[i];
 
 		sk_for_each(s, node, head) {
-			struct atm_vcc *vcc = atm_sk(s);
+			vcc = atm_sk(s);
 
 			purge_vcc(vcc);
 		}