Implement NAPI changes to pcnet32 driver.  Compile default is off.
Listed as experimental.

Len and Don both worked on a NAPI implementation and have both tested
these changes.

An e1000 blasting short packets to the pcnet32 will lockup Don's system
until the receive storm stops.  Without NAPI Len's system watchdog would
expire causing the system to reboot.  With NAPI the system will stay
operational.

Tested ia32 and ppc64.  Tested '970A, '971, '972, '973, '975, '976, and
'978.

The Kconfig changes came from Len.  Don is to blame for all the others.
Signed-off-by: Len Sorensen <lsorense@csclub.uwaterloo.ca>
Signed-off-by: Don Fry <brazilnut@us.ibm.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>