Displays or specifies the port upon which outgoing frames
should be transmitted. This would typically be used where
there are several ports (e.g. multiple receivers) sharing a
common transmitter.
If "destport" is not specified, the current setting is
displayed.
If "destport" is zero (the default setting), frames are
received and transmitted on the same port.
If "destport" is a valid port number, frames which would
normally be transmitted on <port> are transmitted on
"destport" instead.
The minimum abbreviation of this command is TXP.