LUDOC-359 lnet: Update to correct Lnet routings config file

LUDOC-359 lnet:  Update to correct Lnet routings config file

Updated section 15.5 of the manual to use the correct name
for the LNet routing config file.  /etc/sysconfig/lnet_routes.conf
is correct, where *lustre*_routes.conf had been incorrectly
specified.

I also updated this section to adhere to max line width.

Signed-off-by: Joseph Gmitter <joseph.gmitter@intel.com>
Change-Id: I63541395241ab8f01548bb3431bc4b9dfeffcb7c
Reviewed-on: https://review.whamcloud.com/25145
Tested-by: Jenkins
Reviewed-by: Amir Shehata <amir.shehata@intel.com>