[PATCH] pcnet32: set min ring size to 4

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.

- 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>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>