net: ks8851: Set initial carrier state to down

The ks8851 chip's initial carrier state is down. A Link Change Interrupt
is signaled once interrupts are enabled if the carrier is up.

The ks8851 driver has it backwards by assuming that the initial carrier
state is up. The state is therefore misrepresented if the interface is
opened with no cable attached. Fix it.

The Link Change interrupt is sometimes not signaled unless the P1MBSR
register (which contains the Link Status bit) is read on ->ndo_open().
This might be a hardware erratum. Read the register by calling
mii_check_link(), which has the desirable side effect of setting the
carrier state to down if the cable was detached while the interface was
closed.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: Frank Pavlic <f.pavlic@kunbus.de>
Cc: Ben Dooks <ben.dooks@codethink.co.uk>
Cc: Tristram Ha <Tristram.Ha@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>