sqm-scripts: clean up interface selection for hotplugging

sqm-scripts: clean up interface selection for hotplugging

The initial conversion to restart sqm on interfaces it is configured
for in case of (transient) dis- and reappearance was half finished.
These changes clean up the handling of exlicitly passed interfaces
in run.sh: no second argument defaults to all configured interfaces
the alternative is an individual interface name passed as 2nd
argument to run.sh. The first argument either is start or stop.
No argument at all will behave as if start was passed.
Survives light testing...

Signed-off-by: Sebastian Moeller <redacted>