IXIA traffic mac address is set incorrectly

IXIA traffic mac address is set incorrectly

IXIA API sets the src/dst mac of the traffic always into
default value. The `srcmac`/`dstmac` is never set in `traffic_param`
map [1]. Instead the src/dst mac is stored in traffic_param[`outer_l2`].

[1] https://gerrit.opnfv.org/gerrit/gitweb?p=yardstick.git;a=blob;f=yardstick/network_services/traffic_profile/ixia_rfc2544.py;h=44bf2eafc7f8cf03ebd2c8520d316358fe1e5fc2;hb=HEAD#l92

JIRA: YARDSTICK-1423

Change-Id: Iabab7a54404b284d3b95bbea6c8624233c138351
Signed-off-by: Mytnyk, Volodymyr <volodymyrx.mytnyk@intel.com>