ixgbe: cleanup X540 interrupt enablement

We don't need SFP+ plugable support for X540 hardware (copper only) so
don't enable the SFP+ interrupts.

Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>