mm: migrate: hugetlb: putback destination hugepage to active list

Since commit bcc54222 ("mm: hugetlb: introduce page_huge_active")
each hugetlb page maintains its active flag to avoid a race condition
betwe= en multiple calls of isolate_huge_page(), but current kernel
doesn't set the f= lag on a hugepage allocated by migration because the
proper putback routine isn= 't called.  This means that users could
still encounter the race referred to by bcc54222 in this special
case, so this patch fixes it.

Fixes: bcc54222 ("mm: hugetlb: introduce page_huge_active")
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>  [4.1.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>