netfilter: nf_conntrack: add include to fix sparse warning

Include header file to pickup prototype of nf_nat_seq_adjust_hook
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_conntrack_core.c

@@ -48,6 +48,7 @@
 #include <net/netfilter/nf_conntrack_labels.h>
 #include <net/netfilter/nf_nat.h>
 #include <net/netfilter/nf_nat_core.h>
+#include <net/netfilter/nf_nat_helper.h>
 
 #define NF_CONNTRACK_VERSION	"0.5.0"