xena_cont_accuracy_fix: Xena continuous traffic accuracy fixes

xena_cont_accuracy_fix: Xena continuous traffic accuracy fixes

Second patch to help improve Xena continuous traffic accuracy.
Increases delay before gathering statistics to allow packets in
flight to be received. Changes bps and fps to be calculated
based on total bytes and packets received versus capturing the
data while port is transmitting from active statistics.

Sets time limit on ports based on duration.

JIRA: VSPerf-423

Change-Id: I574819694d3141edb539de64bc16dcd6c6fcf489
Signed-off-by: Christian Trautman <ctrautma@redhat.com>