wb840: Remove usage of load_driver_symbols under DEBUG.

This function is not declared in the headers anymore,
and is a deprecated no-op.

drivers/network: Move ethernet drivers to an "ether" subdirectory.

Now that there is also a "tap" driver in here, and the WiFi drivers
are also in a subdirectory, moving the physical ethernet device drivers
to a subdirectory also makes sense.

(Briefly) discussed on the mailing lists.