Update sealevel driver to match current net_device interface:
	- dynamically allocate netdevice and private data.
	- get rid of MOD_INC/DEC
	- if_ptr not used
	- bugfix: not all of board structure was being zeroed.

Note: this driver still doesn't probe() correctly since it just assumes that
if loaded the hardware is there!

Since I don't have one of these boards...
tested it by #ifdef'ing out all the bits that touch actual hardware.