ceph: allow revoking duplicated caps issued by non-auth MDS

Allow revoking duplicated caps issued by non-auth MDS if these caps
are also issued by auth MDS.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
ceph: allocate cap_release message when receiving cap import

When client wants to release an imported cap, it's possible there
is no reserved cap_release message in corresponding mds session.
so __queue_cap_release causes kernel panic.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
ceph: check mds_wanted for imported cap

The MDS may have incorrect wanted caps after importing caps. So the
client should check the value mds has and send cap update if necessary.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
ceph: don't acquire i_mutex ceph_vmtruncate_work

In commit 22cddde104, ceph_get_caps() was moved into ceph_write_begin().
So ceph_get_caps() can be called while i_mutex is locked. If there is
pending vmtruncate, ceph_get_caps() will wait for it to complete, but
ceph_vmtruncate_work() is blocked by the locked i_mutex.

There are several places that call __ceph_do_pending_vmtruncate()
without holding the i_mutex, I think it's OK to not acquire the i_mutex
in ceph_vmtruncate_work()

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>