[rtl8139] Strip CRC from received packets

The rtl8139 driver includes the Ethernet CRC within the received
packet.  All current protocols ignore trailing garbage, but FCoE
requires the frame length to be correct (since the FCoE footer
position is calculated from the end of the packet), so fix the driver
to strip out the CRC.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/net/rtl8139.c

 				 rx_len - wrapped_len );
 			memcpy ( iob_put ( rx_iob, wrapped_len ),
 				 rtl->rx.ring, wrapped_len );
+			iob_unput ( rx_iob, 4 ); /* Strip CRC */
 
 			netdev_rx ( netdev, rx_iob );
 		} else {