ice: don't spam VFs with link messages

Don't send a link message to the VFs unless link actually changes state.
This avoids a small timing hole in some VF drivers that can cause an
apparent TX hang if they receive a link status message at the wrong time.

Although we have fixed the timing hole in the current VF driver, there
are still lots of drivers in the field that have this timing hole. Let's
not fall into it if we can avoid it.

Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>