doc: connectivity: networking: Mention VIRTIO Network device in doc

Add instructions on running echo_server using the VIRTIO Network device
in the QEMU Ethernet documentation.

Signed-off-by: Jakub Klimczak <[email protected]>

Author: Jakub Klimczak

doc/connectivity/networking/qemu_eth_setup.rst

@@ -48,6 +48,8 @@ driver for QEMU connectivity:
   Driver is called ``smsc911x`` in Zephyr source tree.
 * For ``qemu_cortex_a53``, ``Intel(R) PRO/1000 Gigabit Ethernet driver``
   Ethernet driver is selected by default.
+* Additionally, the :zephyr:code-sample:`sockets-echo-server` sample contains
+  overlay files for the VIRTIO Network device on ``qemu_x86_64``.
 
 Step 1 - Create Ethernet interface
 ==================================
@@ -85,6 +87,16 @@ In terminal #2, type:
    :goals: run
    :compact:
 
+Alternatively, if you decided to use the VIRTIO Network device on qemu_x86_64:
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/net/sockets/echo_server
+   :host-os: unix
+   :board: qemu_x86_64
+   :gen-args: -DDTC_OVERLAY_FILE=virtnet.overlay -DEXTRA_CONF_FILE=overlay-virtnet.conf
+   :goals: run
+   :compact:
+
 Exit QEMU by pressing :kbd:`CTRL+A` :kbd:`x`.
 
 .. _`net-tools`: https://github.com/zephyrproject-rtos/net-tools