Indicates the desired speed of the port
in bits per second.
The current operational speed of the port
is determined by ifSpeed.
If the port could not agree with the far end on
port speed, the port will be in auto(2) mode,
which will force the port to transmit in speed
whichever is lower.
Unknown(1) indicates either the port does not
support admin speed, or the admin speed is
none of the defined.