net: dm9k: only read on packet for each call to dm9k_eth_rx()
Some users such as fs/nfs.c just save the pointer to the packet in the
handler and process it after net_poll() returns. This break when more than
one packet is received using the same buffer.
Signed-off-by: Michael Olbrich <m.olbrich@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>