[PATCH v3 7/7] doc: update testpmd command

[Helin Zhang <helin.zhang@intel.com>]

testpmd command of 'tx_vlan' has been modified to support insertion
of both single and dual VLAN IDs. Corresponding update in 'Testpmd
Application User Guide' is added.

Signed-off-by: Helin Zhang <helin.zhang@intel.com>
---
 doc/guides/testpmd_app_ug/testpmd_funcs.rst | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/doc/guides/testpmd_app_ug/testpmd_funcs.rst b/doc/guides/testpmd_app_ug/testpmd_funcs.rst
index 761172e..f1fa523 100644
--- a/doc/guides/testpmd_app_ug/testpmd_funcs.rst
+++ b/doc/guides/testpmd_app_ug/testpmd_funcs.rst
@@ -503,9 +503,19 @@ rx_vxlan_port rm (udp_port) (port_id)
 tx_vlan set
 ~~~~~~~~~~~
 
-Set hardware insertion of VLAN ID in packets sent on a port:
+Set hardware insertion of VLAN IDs in packets sent on a port:
 
-tx_vlan set (vlan_id) (port_id)
+tx_vlan set (port_id) vlan_id[, vlan_id_outer]
+
+.. code-block:: console
+
+    Set a single VLAN ID (5) insertion on port 0.
+
+    tx_vlan set 0 5
+
+    Set double VLAN ID (inner: 2, outer: 3) insertion on port 1.
+
+    tx_vlan set 1 2 3
 
 tx_vlan set pvid
 ~~~~~~~~~~~~~~~~
-- 
1.9.3