[NETFILTER]: add some consts, remove some casts

Make a number of variables const and/or remove unneeded casts.

Signed-off-by: Jan Engelhardt <jengelh@gmx.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/netfilter/xt_mark.c b/net/netfilter/xt_mark.c
index 83ed8067..b8ab794 100644
--- a/net/netfilter/xt_mark.c
+++ b/net/netfilter/xt_mark.c
@@ -60,7 +60,7 @@
 
 static void compat_from_user(void *dst, void *src)
 {
-	struct compat_xt_mark_info *cm = src;
+	const struct compat_xt_mark_info *cm = src;
 	struct xt_mark_info m = {
 		.mark	= cm->mark,
 		.mask	= cm->mask,
@@ -71,7 +71,7 @@
 
 static int compat_to_user(void __user *dst, void *src)
 {
-	struct xt_mark_info *m = src;
+	const struct xt_mark_info *m = src;
 	struct compat_xt_mark_info cm = {
 		.mark	= m->mark,
 		.mask	= m->mask,