netfilter: nft_reject_bridge: Fix powerpc build error

Fix:
net/bridge/netfilter/nft_reject_bridge.c:
In function 'nft_reject_br_send_v6_unreach':
net/bridge/netfilter/nft_reject_bridge.c:240:3:
	error: implicit declaration of function 'csum_ipv6_magic'
   csum_ipv6_magic(&nip6h->saddr, &nip6h->daddr,
   ^
make[3]: *** [net/bridge/netfilter/nft_reject_bridge.o] Error 1

Seen with powerpc:allmodconfig.

Fixes: 523b929d5446 ("netfilter: nft_reject_bridge: don't use IP stack to reject traffic")
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/netfilter/nft_reject_bridge.c

@@ -18,6 +18,7 @@
 #include <net/netfilter/ipv6/nf_reject.h>
 #include <linux/ip.h>
 #include <net/ip.h>
+#include <net/ip6_checksum.h>
 #include <linux/netfilter_bridge.h>
 #include "../br_private.h"