LU-3534 ptlrpc: mbits is sent within ptlrpc_body

LU-3534 ptlrpc: mbits is sent within ptlrpc_body

ptlrpc is using rq_xid as matchbits of bulk data, which means it
has to change rq_xid for bulk resend to avoid several bulk data
landing into the same buffer from different resends.

This patch uses one of reserved __u64 of ptlrpc_body to transfer
mbits to peer, matchbits is now separated from xid. With this change,
ptlrpc can keep rq_xid unchanged on resend, it only updates matchbits
for bulk data.

This protocol change is only applied if both sides of connection have
OBD_CONNECT_BULK_MBITS, otherwise, ptlrpc still uses old approach and
update xid while resending bulk.

Signed-off-by: Liang Zhen <liang.zhen@intel.com>
Change-Id: Ide0b3f490368babeb6ac1b4ea6953f8f9aacf81a
Reviewed-on: http://review.whamcloud.com/15421
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>