[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>
diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
index eb330a4..532425d 100644
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c
@@ -663,7 +663,7 @@
 			break;
 		}
 		gsf = kmalloc(optlen,GFP_KERNEL);
-		if (gsf == 0) {
+		if (!gsf) {
 			retv = -ENOBUFS;
 			break;
 		}