Teach SQM hotplug tricks

Teach SQM hotplug tricks

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...