ionic: better handling of RESET event

When IONIC_EVENT_RESET is received, we only need to start the
fw_down process if we aren't already down, and we need to be
sure to set the FW_STOPPING state on the way.

If this is how we noticed that FW was stopped, it is most
likely from a FW update, and we'll see a new FW generation.
The update happens quickly enough that we might not see
fw_status==0, so we need to be sure things get restarted when
we see the fw_generation change.

Fixes: d2662072 ("ionic: monitor fw status generation")
Signed-off-by: Shannon Nelson <snelson@pensando.io>
Signed-off-by: David S. Miller <davem@davemloft.net>