net/mlx4_core: Use msi_x module param to limit num of MSI-X irqs

Extend the boolean interpretation of msi_x module parameter
to numerical, as follows:

0   - Don't use MSI-X.
1   - Use MSI-X, driver decides the num of MSI-X irqs.
>=2 - Use MSI-X, limit number of MSI-X irqs to msi_x.
      In SRIOV, this limits the number of MSI-X irqs per VF.

Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Cc: Ajaykumar Hotchandani <ajaykumar.hotchandani@oracle.com>
Reviewed-by: Ajaykumar Hotchandani <ajaykumar.hotchandani@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>