NSB: fix trex config to use dpdk port number

NSB: fix trex config to use dpdk port number

From some reason Heat/Neutron is now creating
interfaces such that xe0 and xe1 are swapped.

xe0  fa:16:3e:38:c7:66  0000:00:05.0
xe1  fa:16:3e:2f:f3:e2  0000:00:03.0

this causes the DPDK port numbering to be swapped.

xe0 is DPDK port 1 because it has higher PCI address
xe1 is DPDK port 0 because it has lower PCI address.

The VNF is configured correctly because it uses DPDK port numbers,
whereas TRex was using interface list ordering.

Modify trex_cfg.yaml to use DPDK port ordering.  This also
requires running generate_cfg() after setup() in instantiate()

+------------------------------------+-------------------+------------------------------+--------+
| Name                               | MAC Address       | Fixed IP Addresses           | Status |
+------------------------------------+-------------------+------------------------------+--------+
| vnf_0.yardstick-af5ccb47-xe0-port  | fa:16:3e:66:a5:e4 | ip_address='10.1.0.7',       | ACTIVE |
| vnf_0.yardstick-af5ccb47-mgmt-port | fa:16:3e:fa:98:fe | ip_address='10.0.1.10',      | ACTIVE |
| tg_0.yardstick-af5ccb47-xe1-port   | fa:16:3e:2f:f3:e2 | ip_address='10.1.1.9',       | ACTIVE |
| vnf_0.yardstick-af5ccb47-xe1-port  | fa:16:3e:f3:1d:f5 | ip_address='10.1.1.4',       | ACTIVE |
|                                    | fa:16:3e:e3:8c:65 | ip_address='10.0.1.1',       | ACTIVE |
|                                    | fa:16:3e:ff:d1:b7 | ip_address='11.191.14.110',  | N/A    |
| tg_0.yardstick-af5ccb47-xe0-port   | fa:16:3e:38:c7:66 | ip_address='10.1.0.8',       | ACTIVE |
|                                    | fa:16:3e:ff:53:5f | ip_address='11.191.14.101',  | DOWN   |
|                                    | fa:16:3e:23:5d:2c | ip_address='10.0.1.2',       | ACTIVE |
| tg_0.yardstick-af5ccb47-mgmt-port  | fa:16:3e:7a:df:4e | ip_address='10.0.1.5',       | ACTIVE |
|                                    | fa:16:3e:22:65:36 | ip_address='11.191.14.109',  | N/A    |
+------------------------------------+-------------------+------------------------------+--------+

/sys/devices/pci0000:00/0000:00:03.0/virtio0/net/ens3/address:fa:16:3e:2f:f3:e2
/sys/devices/pci0000:00/0000:00:05.0/virtio2/net/ens5/address:fa:16:3e:38:c7:66

Change-Id: Iaef2c7d9a5af7f45bd805a8ad6ee545ce0495cb1
Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>
(cherry picked from commit 7ed018cddf88ac1c5a92f71fa5e421e66d259bc0)