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/ipv4.h

@@ -43,7 +43,6 @@ struct netns_ipv4 {
 	struct xt_table		*nat_table;
 	struct hlist_head	*nat_bysource;
 	unsigned int		nat_htable_size;
-	int			nat_vmalloced;
 #endif
 
 	int sysctl_icmp_echo_ignore_all;