LUDOC-253 lnet: Update and correct routerstat info

LUDOC-253 lnet: Update and correct routerstat info

Correct the description of routerstat output values,
add a description of additional lines printed when
providing an interval value, and add an example of
routerstat output.

Signed-off-by: James Nunez <james.a.nunez@intel.com>
Change-Id: I36ee7a12b5b4e32e8b70a7cab491cd9e9addfcee
Reviewed-on: http://review.whamcloud.com/11350
Tested-by: Jenkins
Reviewed-by: Amir Shehata <amir.shehata@intel.com>
Reviewed-by: Richard Henwood <richard.henwood@intel.com>