Add simple VxLAN decapsulation performance test

Measure OVS DPDK VXLAN decapsulation performance.
The DUT is configured as a VTEP (VXLAN Tunnel Endpoint)
which performs decapsulation of frames and sends traffic to
the 2nd traffic generator port.

This test is unidirectional.

Recent changes:
* Userguide update
* Move src/dstport from L2 to L4 (conf, TCL)
* Fix 'TestCase' object has no attribute '_tunnel_operation' error when
  running non overlay tests
* Fix merge conflict
* Move doc to docs/userguide/integration.rst
* Add setting of DUT_NIC1_MAC and setting of other
  variables to docs/userguide/integration.rst

Change-Id: Ia44f8888ef727831543c80f5c98c866686c5c92c
JIRA: VSPERF-190
Signed-off-by: Dino Simeon Madarang <dino.simeonx.madarang@intel.com>
Signed-off-by: Robert Wojciechowicz <robertx.wojciechowicz@intel.com>
Signed-off-by: Timo Puha <timox.puha@intel.com>
Reviewed-by: Maryam Tahhan <maryam.tahhan@intel.com>
Reviewed-by: Billy O Mahony <billy.o.mahony@intel.com>
Reviewed-by: Martin Klozik <martinx.klozik@intel.com>
Reviewed-by: Al Morton <acmorton@att.com>
Reviewed-by: Brian Castelli <brian.castelli@spirent.com