If we send a layoutreturn asynchronously before close, the close
might reach server first and layoutreturn would fail with BADSTATEID
because there is nothing keeping the layout stateid alive.

Also do not pretend sending layoutreturn if we are not.
Signed-off-by: NPeng Tao <tao.peng@primarydata.com>
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>