alx: enable msi-x interrupts by default

Remove the module parameter to enable msi-x support and enable msi-x
interrupts unconditionally by default. This is a preparatory step to enable
multi queue support by default, because this is only working with msi-x
interrupts.

Signed-off-by: Tobias Regnery <tobias.regnery@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>