Xena_cont_accuracy: Modify continuous from duration to packet limit

Xena_cont_accuracy: Modify continuous from duration to packet limit

First of a few patches planned to help increase Xena continuous
traffic accuracy. Modifies port limits to packet calculated limits
versus time based limits which can be wildly inaccurate. Also
modifies some port settings to be more inline with how rfc2544
settings are applied on Xena. Increased time delay by one
second to allow packets to finish transmitting before stat
collection occurs.

JIRA: VSPerf-423

Change-Id: I214b13d743a84a0733e885ccfc5bdd57812d7104
Signed-off-by: Christian Trautman <ctrautma@redhat.com>