net: mvpp2: add buffer header handling in RX

If Link Partner sends frames larger than RX buffer size, MAC mark it
as oversize but still would pass it to the Packet Processor.
In this scenario, Packet Processor scatter frame between multiple buffers,
but only a single buffer would be returned to the Buffer Manager pool and
it would not refill the poll.

Patch add handling of oversize error with buffer header handling, so all
buffers would be returned to the Buffer Manager pool.

Fixes: 3f518509

 ("ethernet: Add new driver for Marvell Armada 375 network unit")
Reported-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Stefan Chulski <stefanc@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>