staging: lustre: osc: Automatically increase the max_dirty_mb

When RPC size or the max RPCs in flight is increased, the actual
limit might be max_dirty_mb. This patch automatically increases
the max_dirty_mb value at connection time and when the related
values are tuned manually by proc file system.

this patch also changes the unit of "cl_dirty" and "cl_dirty_max"
in client_obd from byte to page.

Signed-off-by: Li Xi <lixi@ddn.com>
Signed-off-by: Hongchao Zhang <hongchao.zhang@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-4933
Reviewed-on: http://review.whamcloud.com/10446


Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>