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>