netfilter: nf_conntrack: allow nf_ct_alloc_hashtable() to get highmem pages

commit ea781f19 (use SLAB_DESTROY_BY_RCU and get rid of call_rcu())
did a mistake in __vmalloc() call in nf_ct_alloc_hashtable().

I forgot to add __GFP_HIGHMEM, so pages were taken from LOWMEM only.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Patrick McHardy <kaber@trash.net>

net/netfilter/nf_conntrack_core.c

@@ -1312,7 +1312,8 @@ void *nf_ct_alloc_hashtable(unsigned int *sizep, int *vmalloced, int nulls)
 	if (!hash) {
 		*vmalloced = 1;
 		printk(KERN_WARNING "nf_conntrack: falling back to vmalloc.\n");
-		hash = __vmalloc(sz, GFP_KERNEL | __GFP_ZERO, PAGE_KERNEL);
+		hash = __vmalloc(sz, GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO,
+				 PAGE_KERNEL);
 	}
 
 	if (hash && nulls)