netfilter: nf_conntrack: use is_vmalloc_addr()

Use is_vmalloc_addr() in nf_ct_free_hashtable() and get rid of
the vmalloc flags to indicate that a hash table has been allocated
using vmalloc().

Signed-off-by: Patrick McHardy <kaber@trash.net>

include/net/netns/conntrack.h

@@ -28,8 +28,6 @@ struct netns_ct {
 	struct ctl_table_header	*acct_sysctl_header;
 	struct ctl_table_header	*event_sysctl_header;
 #endif
-	int			hash_vmalloc;
-	int			expect_vmalloc;
 	char			*slabname;
 };
 #endif