net: ena: change num_queues to num_io_queues for clarity and consistency

Most places in the code refer to the IO queues as io_queues and not
simply queues. Examples - max_io_queues_per_vf, ENA_MAX_NUM_IO_QUEUES,
ena_destroy_all_io_queues() etc..

We are also adding the new max_num_io_queues field to struct ena_adapter
in the following commit.

The changes included in this commit are:
struct ena_adapter->num_queues => struct ena_adapter->num_io_queues

Signed-off-by: Arthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: Sameeh Jubran <sameehj@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>