r6040: check PHY status when bringing interface up

This patch makes the driver properly initialize the PHY
status if not correctly set by the bootloader/BIOS.
It prevents some boards to bring up the link on boot.

Signed-off-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: David S. Miller <davem@davemloft.net>