LUDOC-368 lnet: Dynamic Discovery documentation

LUDOC-368 lnet:  Dynamic Discovery documentation

This patch adds documentation for the dynamic peer discovery
feature added in Lustre 2.11.0 by LU-9480.

Documentation is added to the LNet configuration section of the
manual.

Also, this patch does some refactoring of the affected
ConfiguringLNet.xml content file to use descriptive XML
ID tags instead of random integer strings as well as
fixing numerous 80 column length style issues in the
file.

Signed-off-by: Joseph Gmitter <joseph.gmitter@intel.com>
Change-Id: Iba9644f5777f0930bac7d0583072e651d04a222a
Reviewed-on: https://review.whamcloud.com/31735
Reviewed-by: Amir Shehata <amir.shehata@intel.com>
Tested-by: Jenkins
Reviewed-by: James Nunez <james.a.nunez@intel.com>