BUG/MEDIUM: stream_interface: Don't add SI_FL_ERR the state is < SI_ST_CON.

BUG/MEDIUM: stream_interface: Don't add SI_FL_ERR the state is < SI_ST_CON.

Only add SI_FL_ERR if the stream_interface is connected, or is attempting
a connection. We may get there because the stream_interface's tasklet
was woken up, but before it actually runs, process_stream() may be called,
detect that there were an error, and change the state of the stream_interface
to SI_ST_TAR. When the stream_interface's tasklet then run, the connection
may still have CO_FL_ERROR, but that error was already accounted for, so
just ignore it.

This should be backported to 2.0.