ixgbe: do not report 2.5 Gbps as supported

ixgbe: do not report 2.5 Gbps as supported

Orabug: 23177316

Some X550 devices can connect at 2.5Gbps during fail-over, but only
with certain link partners. Also setting the advertised speed will
not work so we do not report it as supported to avoid confusion.

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
(cherry picked from commit d3428001c58dce10af624e889667c7862320390a)
Signed-off-by: Brian Maly <brian.maly@oracle.com>