fix: IPV6 packet generation, packet loss reporting

fix: IPV6 packet generation, packet loss reporting

UDP and IP packet length and source UDP port and destination UDP port
were wrongly set for IPv6 packets.
In the *.test files, there is now an optional boolean field (ipv6) in
the [TestParameters] section. When set to true, the generator will use
the IPv6 packet layout to place the right values at the proper offset
in the packet. If not present or set to false, the IPv4 layout will be
used. Note also that packet size needs to be at least 84 bytes for IPV6
traffic since we need space for latency and other information in each
packet.
Packet loss ratio is now printed as a percentage of the total packets
sent.

Change-Id: I2136e87f3032348ae95b69052be7da8461c6303c
Signed-off-by: Luc Provoost <luc.provoost@intel.com>