dpif-netdev: Change definitions of 'idle' & 'processing' cycles

dpif-netdev: Change definitions of 'idle' & 'processing' cycles

Instead of counting all polling cycles as processing cycles, only count
the cycles where packets were received from the polling.

Signed-off-by: Georg Schmuecking <georg.schmuecking@ericsson.com>
Signed-off-by: Ciara Loftus <ciara.loftus@intel.com>
Co-authored-by: Georg Schmuecking <georg.schmuecking@ericsson.com>
Acked-by: Kevin Traynor <ktraynor@redhat.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Ian Stokes <ian.stokes@intel.com>
Tested-by: Ian Stokes <ian.stokes@intel.com>
Acked-by: Darrell Ball <dlu998@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>