[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/ipv6/netfilter/ip6t_REJECT.c b/net/ipv6/netfilter/ip6t_REJECT.c
index 8639a059..4df07f0 100644
--- a/net/ipv6/netfilter/ip6t_REJECT.c
+++ b/net/ipv6/netfilter/ip6t_REJECT.c
@@ -159,7 +159,7 @@
 	tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr,
 				      &ipv6_hdr(nskb)->daddr,
 				      sizeof(struct tcphdr), IPPROTO_TCP,
-				      csum_partial((char *)tcph,
+				      csum_partial(tcph,
 						   sizeof(struct tcphdr), 0));
 
 	nf_ct_attach(nskb, oldskb);