MRP-459 ptlrpc: Allow clients reconnect with RPCs in process

Since not letting clients with pending RPCs to reconnect caused a lot
of problems, this patch allows such a reconnection and would only
refuse to process requests with the same xids that are already being
processed. This patch is a port of LU-793 to b_neo_stable (2.2)
Requests from Andreas were added also.

Signed-off-by: Iurii Golovach <iurii_golovach@xyratex.com>
Signed-off-by: Andriy Skulysh <Andriy_Skulysh@xyratex.com>
Change-Id: I954e43aa0242304707d6b0600df4ad229fb47227
Reviewed-on: http://morpheus.xyus.xyratex.com:8443/231
Tested-by: Jenkins
Reviewed-by: Alexey Lyashkov <Alexey_Lyashkov@xyratex.com>
Tested-by: Alexander Lezhoev <Alexander_Lezhoev@xyratex.com>
Reviewed-by: Denis Kondratenko <Denis_Kondratenko@xyratex.com>
Revert "MRP-757: ldiskfs fix procfs access to mb groups."

This reverts commit ba49c5bb2111d1c707a0a2c0e6adc54bb22c1d99.
Revert "MRP-602 LDISKFS procfs entries for mballoc"

This reverts commit 996fbaa39ddef32a24a7d670b2f3ccf4d80028a9.