LU-11874 rpc: Update command to persisently set brw_size

LU-11874 rpc: Update command to persisently set brw_size

This patch updates the large bulk IO (16MB RPC) section
to use set_param -P in persistently setting brw_size
and max_pages_per_rpc as the current conf_param command
does not work with wildcards.

Signed-off-by: Joseph Gmitter <jgmitter@whamcloud.com>
Change-Id: I1cfec45a032b3bc4bf97c14ef6db2a3f0901194f
Reviewed-on: https://review.whamcloud.com/34193
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Stephan Thiell <sthiell@stanford.edu>