1. When processing Rx packets, making sure that get offset of ring
does not cross the put offset.

2. when NAPI is not in use a new spinlock(put_lock) is used to make
sure accessing put offset of ring is atomic.

3. Also introduced a new vaiable put_pos in nic_t to keep track of
absolute position of the put pointer of Rx ring.

4. When NAPI is used, fill_rx_buffer is not called from the interrupt
handler(s2io_isr) .

5. In s2io_poll, decrementing packets processed is done inside the
while loop unlike out side it as was being done last time.
Signed-off-by: Raghavendra Koushik <raghavendra.koushik@s2io.com>
Signed-off-by: Ravinandan Arakali <ravinandan.arakali@s2io.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>