Adding support for echo option if telnet commands are supported. This is
useful when the telnet client is in character mode. It allows to use the
arrow keys, ctrl-c and more. Something to keep in mind is that when
character mode is turned on by the client, network traffic is
considerably increased as each typed character is sent over the wire.
Note: echo mode is only supported if SHELL_TELNET_SUPPORT_COMMAND is
enabled.
Signed-off-by: David Corbeil <david.corbeil@dynon.com>
724c162821