netfilter: nft_payload: Remove duplicated include in nft_payload.c

Fix following checkincludes.pl warning:
./net/netfilter/nft_payload.c: linux/ip.h is included more than once.
Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_payload.c

@@ -22,7 +22,6 @@
 #include <linux/icmpv6.h>
 #include <linux/ip.h>
 #include <linux/ipv6.h>
-#include <linux/ip.h>
 #include <net/sctp/checksum.h>
 
 static bool nft_payload_rebuild_vlan_hdr(const struct sk_buff *skb, int mac_off,