fuse: convert fuse_writepage_need_send to take a folio

fuse: convert fuse_writepage_need_send to take a folio

fuse_writepage_need_send is called by fuse_writepages_fill() which
already has a folio.  Change fuse_writepage_need_send() to take a folio
instead, add a helper to check if the folio range is under writeback and
use this, as well as the appropriate folio helpers in the rest of the
function.  Update fuse_writepage_need_send() to pass in the folio
directly.

Reviewed-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>