hugetlb: move refcounting in hugepage allocation inside hugetlb_lock

Currently alloc_huge_page() raises page refcount outside hugetlb_lock.
but it causes race when dequeue_hwpoison_huge_page() runs concurrently
with alloc_huge_page().
To avoid it, this patch moves set_page_refcounted() in hugetlb_lock.

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>