T-REX: change relative rate values to absolute units

Instead of using realative values expressed in percentage
of linerate rather use absolute values to assure consistency
of results across NICs with various speeds (10G, 40G, 100G, ...)

Change-Id: Ifd455d823e80002c277deaf8cb8295c81b59bf4a
Signed-off-by: Miroslav Miklus <mmiklus@cisco.com>