Shorewall: start and enable interfaces all in hotplug

Shorewall: start and enable interfaces all in hotplug

Using shorewall-lite {en|dis}able instead of completely restarting
Shorewall is much more efficient.

But it also makes sense to move the starting of Shorewall from init
to an interface hotplug event.  The "lan" interface should be a good
indicator that networking it ready.  Besides, Shorewall won't start
until br-lan is available.

Signed-off-by: Brian J. Murrell <brian@interlinx.bc.ca>