atl1c: improve link detection reliability on Mikrotik 10/25G NIC

Mikrotik 10/25G NIC emulates the MDIO accesses, but the emulation is
not 100% reliable - the MDIO ops occasionally can timeout.

This adds a reliable way of detecting link on Mikrotik 10/25G NIC.

Signed-off-by: Gatis Peisenieks <gatis@mikrotik.com>
Signed-off-by: David S. Miller <davem@davemloft.net>