pcmcia ether drivers can't be unloaded

It looks like pcmica modular ether (example orinoco) can never be manually unloaded because
module refcount is always 1. This comes from the owner field in the pcmcia_driver.owner
being set.

One fix is to not set owner field but then there is a hot plug/module remove
race. But the right fix seems to fix up pcmcia to be a true bus in the driver
model and have the same hotplug as other buses; usb and pci don't have the problem.