interface mirror options are changed.

two paragraphs are defined about the mirror option, removed the paragraph
having the older cli structure.

(cherry picked from commit c7d52cf)

docs/_include/interface-mirror.txt

@@ -1,7 +1,10 @@
 SPAN port mirroring can copy the inbound/outbound traffic of the interface to
 the specified interface, usually the interface can be connected to some special
 equipment, such as behavior control system, intrusion detection system and
-traffic collector, and can copy all related traffic from this port
+traffic collector, and can copy all related traffic from this port.
+The benefit of mirroring the traffic is that the application is isolated from 
+the source traffic and so application processing does not affect the traffic 
+or the system performance.
 
 VyOS uses the `mirror` option to configure port mirroring. The configuration
 is divided into 2 different directions. Destination ports should be configured

docs/configuration/interfaces/ethernet.rst

@@ -53,21 +53,6 @@ Ethernet options
    VyOS default will be `auto`.
 
 
-.. cfgcmd:: set interfaces ethernet <interface> mirror <interface>
-
-  Use this command to mirror the inbound traffic from one Ethernet interface to
-  another interface. This feature is typically used to provide a copy of traffic
-  inbound on one interface to a system running a monitoring or IPS application
-  on another interface. The benefit of mirroring the traffic is that the
-  application is isolated from the source traffic and so application processing
-  does not affect the traffic or the system performance.
-
-  Example:
-
-  .. code-block:: none
-
-    set interfaces ethernet eth0 mirror eth1
-
 Offloading
 ----------