ceph: call handle_cap_grant() for cap import message

If client sends cap message that requests new max size during
exporting caps, the exporting MDS will drop the message quietly.
So the client may wait for the reply that updates the max size
forever. call handle_cap_grant() for cap import message can
avoid this issue.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Signed-off-by: Sage Weil <sage@inktank.com>
(cherry picked from commit 0e5e1774a92e6fe9c511585de8f078b4c4c68dbb)
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>