sys/console: Fix RTT input handling with massive output stream
sys/console: Fix RTT input handling with massive output stream

console_handle_char may return negative value in case console
can't be locked. It can happen when a lot of data is being
transmitted out.
If this happened on first negative value returned from
console_handle_char RTT input was disable by not starting
timer for polling again.

This change makes timer active on console_handle_char failure.

mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core