wifi: shell: Map negative status code to valid status codes

The negative status code is actually the errno which we might
get returned from lower levels. For example if user sets -t
(timeout) option, the -ETIMEDOUT might be returned. In this case
map the errno value to connection timeout status value.

Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>