staging: lustre: obdclass: variable llog chunk size

Do not use fix LLOG_CHUNK_SIZE (8192 bytes), and
it will get the llog_chunk_size from llog_log_hdr.
Accordingly llog header will be variable too, so
we can enlarge the bitmap in the header, then
have more records in each llog file.

Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: wang di <di.wang@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-6602
Reviewed-on: http://review.whamcloud.com/14883


Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>