net: mii: check phy advertising register when geting link status

When phy autoneg on, the link speed and duplex should be
determined by phy advertising register and
phy link partner ability register.
Check phy advertising register when geting phy link speed and
duplex if autoneg on.

Signed-off-by: Dongpo Li <lidongpo@hisilicon.com>
Cc: Joe Hershberger <joe.hershberger@ni.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>