ipv4: coding style: comparison for equality with NULL

The ipv4 code uses a mixture of coding styles. In some instances check
for NULL pointer is done as x == NULL and sometimes as !x. !x is
preferred according to checkpatch and this patch makes the code
consistent by adopting the latter form.

No changes detected by objdiff.

Signed-off-by: Ian Morris <ipm@chirality.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/gre_offload.c b/net/ipv4/gre_offload.c
index 51973dd..9358f11 100644
--- a/net/ipv4/gre_offload.c
+++ b/net/ipv4/gre_offload.c
@@ -149,7 +149,7 @@
 
 	rcu_read_lock();
 	ptype = gro_find_receive_by_type(type);
-	if (ptype == NULL)
+	if (!ptype)
 		goto out_unlock;
 
 	grehlen = GRE_HEADER_SECTION;