FEC: Do not pass unaligned buffer to network stack

FEC: Do not pass unaligned buffer to network stack

Do not pass unaligned RX buffer to the upper layers. The upper layer,
especially in the ARP case, recycles the buffer and passes it back into
the FEC, into it's TX path. With caches enabled, the FEC hangs on this
from time to time.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Benoit Thebaudeau <benoit.thebaudeau@advans>
Cc: Eric Nelson <eric.nelson@boundarydevices.com>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Joe Hershberger <joe.hershberger@ni.com>
Tested-by: Fabio Estevam <fabio.estevam@freescale.com>