phylink: restart 802.3z negotiation when starting net device

Restart 802.3z negotiation when the net device is brought up to ensure
that the link partner has our current link modes.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>