LU-1164 o2iblnd: param to tune number of kib scheduler threads

LU-1164 o2iblnd: param to tune number of kib scheduler threads

This patch gives the ability to control the number of kib scheduler
threads launched by the ko2iblnd module, via a kernel module option.

Indeed, we can have some situations where the default threads number
is not appropriate. The default value is to create as many threads as
the number of CPU cores.

On certain platforms, we have noticed a performance penalty
when running too many kib scheduler threads.

Signed-off-by: Sebastien Buisson <sebastien.buisson@bull.net>
Change-Id: I2f7baa2f9bc9350502d1a0738c8e72777b57fa57
Reviewed-on: http://review.whamcloud.com/3047
Tested-by: Hudson
Reviewed-by: Liang Zhen <liang@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Doug Oucharek <doug@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>