ceph: set timeout conditionally in __cap_delay_requeue
__cap_delay_requeue could be invoked through ceph_check_caps when there
exists caps that needs to be sent and are delayed by "i_hold_caps_min"
or "i_hold_caps_max". If __cap_delay_requeue sets timeout unconditionally,
there could be a chance that some "wanted" caps can not be release for a
long since their timeouts are reset every time they get delayed.