NFSv4: We must set NFS_OPEN_STATE flag in nfs_resync_open_stateid_locked

Otherwise, nfs4_select_rw_stateid() will always return the zero stateid
instead of the correct open stateid.

Fixes: f95549cf ("NFSv4: More CLOSE/OPEN races")
Cc: stable@vger.kernel.org # 4.0+
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>