s390/qeth: clean up QETH_PROT_* naming

The QETH_PROT_* naming is shared among two unrelated areas - one is
the MPC-level protocol identifiers, the other is the qeth_prot_version
enum.

Rename the MPC definitions to use QETH_MPC_PROT_*.

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