[PATCH] mv643xx_eth: Always free completed tx descs on tx interrupt

Fix the tx interrupt handler to free completed tx descriptors even
when NAPI is enabled.  Otherwise, the tx queue would fill up resulting
in poor performance and "NETDEV WATCHDOG: <iface>: transmit timed out"
messages.

Signed-off-by: Brent Cook <bcook@bpointsys.com>
Signed-off-by: Dale Farnsworth <dale@farnsworth.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>