void e100_start_ru (struct e100_private * bdp);
This routine checks the status of the 82557's receive unit(RU), and starts the RU if it was not already active. However, before restarting the RU, the driver gives the RU the buffers it freed up during the servicing of the ISR. If there are no free buffers to give to the RU, (i.e. we have reached a no resource condition) the RU will not be started till the next ISR.