s390/qeth: support per-frame invalidation

Each RX buffer may contain up to 64KB worth of data. In case the device
needs to discard a packet _after_ already having reserved space for it
in the buffer, the whole buffer gets set to ERROR state. As the buffer
might contain any number of good packets, this can result in collateral
packet loss.

qeth can provide relief by enabling per-frame invalidation. The RX
buffer is then presented as usual, we just need to spot & drop any
individual packet that was flagged as invalid.

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>