ixgbe: Configure advertised speeds correctly for KR/KX backplane

This patch ensures that the advertised link speeds are configured
for X553 KR/KX backplane.  Without this patch the link remains at
1G when resuming from low power after being downshifted by LPLU.

Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>