mds: journal backtrace update in EMetaBlob::fullbit

mds: journal backtrace update in EMetaBlob::fullbit

Current way to journal backtrace update is set EMetaBlob::update_bt
to true. The problem is that an EMetaBlob can include several inodes.
If an EMetaBlob's update_bt is true, journal replay code has to queue
backtrace updates for all inodes in the EMetaBlob.

This patch adds two new flags to class EMetaBlob::fullbit, make it be
able to journal backtrace update.

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