ibmvnic: Rename IBMVNIC_MAX_TX_QUEUES to IBMVNIC_MAX_QUEUES

This value denotes the maximum number of TX queues but is used
to allocate both RX and TX queues.

Signed-off-by: Thomas Falcon <tlfalcon@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>