net: phy: turn carrier off on phy attach

The operstate of a networking device initially IF_OPER_UNKNOWN aka
"unknown", updated on carrier state changes (with carrier state being on
by default). This means it will stay unknown unless the carrier state
goes to off at some point, which is not the case if the phy is already
up/connected at startup.

Explicitly turn off the carrier on phy attach, leaving the phy state
machine to turn the carrier on when it has done the initial negotiation.

Signed-off-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>