Add -D/--diff-stat: instead of immediately displaying total
collected NFS stats and exiting, nfsstat will take a snapshot of current
statistics and pause until the user hits ^C, at which point it takes a
second snapshot and then prints out the difference of the two; i.e.,
only the statistics collected during the pause.
Signed-off-by: David M. Richter <richterd@citi.umich.edu> Signed-off-by: Neil Brown <neilb@suse.de>