Fixes #1202.

Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>

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 <moeller0@gmx.de>

During system start up pppoe devices seem to receice ifup events before
the interface actually exists. This commit makes sqm's run.sh script
test whether the sys files for an interface exist before actually trying
to start an SQM instance on an interface. This seems to nicely avoid
starting on an not fully established pppoe interface and avoids a number
of error messages during startup.

In addition, debug logging is disabled.

Signed-off-by: Sebastian Moeller <moeller0@gmx.de>

Some interfaces like wan-pppoe go away, when the ppp connection is lost
and get recreated once the link is established again. SQM now
has its own hotplug script to re-enable itself on the interfae just hotplugged.
SQM will not touch other instances of itself running on other interfaces
if called by hotplug.d. The implementation now allows this functionality by
calling run.sh like:
/usr/lib/sqm/run.sh interface YOUR_INTERFACE_NAME_HERE
e.g.: /usr/lib/sqm/run.sh interface ge00-pppoe
If called with a specific interface SQM will only try to disable itself
on that interface to clean up all left over state and the re-enable
itself on just that interface. Hopefully that allows for better service
with instable interfaces like pppoe. The current code passes a simple manual
stop start test of the ge00-pppoe interface from the GUI and does seem
to do the right thing, at least on cerowrt 3.10.50-1...