Hi,

Don Fry reminded me that the pcnet32_loopback_test() asssumes the ring 
size is no less than 4. The minimum ring size was changed to 4 in 
pcnet32_set_ringparam() to allow the loopback test to work unchanged.

Changelog:
- Set minimum ring size to 4 to allow loopback test to work unchanged
- Moved variable init_block to first field in struct pcnet32_private

Signed-off-by: Hubert WS Lin <wslin@tw.ibm.com>