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.

Fixes: http://tracker.ceph.com/issues/36369


Signed-off-by: Xuehan Xu <xuxuehan@360.cn>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>