LU-6356 ptlrpc: add a 'enc_pool_max_memory_mb' module param

LU-6356 ptlrpc: add a 'enc_pool_max_memory_mb' module param

Create a new 'enc_pool_max_memory_mb' module param for ptlrpc.
It is used to set max memory used by encoding pools, in MB.
By default encoding pools will use at max 1/8 of total physical
memory, but it appears to be too few under some circumstances.

Signed-off-by: Sebastien Buisson <sebastien.buisson@bull.net>
Change-Id: If431ba082eec4bc2c4f2131d4b6b5b7028a3a569
Reviewed-on: http://review.whamcloud.com/15069
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>