net: fec: restart the FEC when PHY speed changes

Proviously we would only restart the FEC when PHY link or duplex state
changed. PHY does not always bring down the link for speed changes, in
which case we would not detect any change and keep FEC running.

Switching link speed without restarting the FEC results in the FEC being
stuck in an indefinite state, generating error conditions for every
packet.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>