ixgbe: add Linux NICS mailing list to contact info

This patch updates the contact information on the ixgbe driver files so
that every file includes the Linux NICS address, as it is still used,
but only a few of the files mentioned it.

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>