netfilter: nf_conntrack_extend: introduce __nf_ct_ext_exist()

some users of nf_ct_ext_exist() know ct->ext isn't NULL. For these users, the
check for ct->ext isn't necessary, the function __nf_ct_ext_exist() can be
used instead.

the type of the return value of nf_ct_ext_exist() is changed to bool.

Signed-off-by: Changli Gao <xiaosuo@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>
diff --git a/include/net/netfilter/nf_conntrack_extend.h b/include/net/netfilter/nf_conntrack_extend.h
index 32d15bd..0772d29 100644
--- a/include/net/netfilter/nf_conntrack_extend.h
+++ b/include/net/netfilter/nf_conntrack_extend.h
@@ -28,9 +28,14 @@
 	char data[0];
 };
 
-static inline int nf_ct_ext_exist(const struct nf_conn *ct, u8 id)
+static inline bool __nf_ct_ext_exist(const struct nf_ct_ext *ext, u8 id)
 {
-	return (ct->ext && ct->ext->offset[id]);
+	return !!ext->offset[id];
+}
+
+static inline bool nf_ct_ext_exist(const struct nf_conn *ct, u8 id)
+{
+	return (ct->ext && __nf_ct_ext_exist(ct->ext, id));
 }
 
 static inline void *__nf_ct_ext_find(const struct nf_conn *ct, u8 id)