ixgbe: add comment noting recalculation of queues

Since we previously called ixgbe_set_num_queues just prior to attempting
to set our interrupt scheme, it may be non obvious why we have to call
it again inside the function. Add a comment which helps make it more
obvious that we are resetting features based on the fact that we do not
have MSI-X enabled, and cannot use the previous settings.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>