NFSv4.1: Clear NFS_LAYOUT_BULK_RECALL when the layout segments are freed

Once all the affected layout segments have been freed up, clear the
NFS_LAYOUT_BULK_RECALL flag so that we can reuse the pnfs_layout_hdr

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>