LU-3788 man: add "lctl set_param -P" to lctl.8 man page

LU-3788 man: add "lctl set_param -P" to lctl.8 man page

lctl set_param -P has been added with LU-3155.

This add information about the command to the man page.

Xyratex-bug-id: MRP-272
Signed-off-by: Artem Blagodarenko <artem_blagodarenko@xyratex.com>
Change-Id: I63197836cbd3ce287f9cda33ab292e1e105c7ee8
Reviewed-on: http://review.whamcloud.com/7452
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>