sfc: Move PHY software state initialisation from init() into probe()

This prevents efx->link_advertising from being blatted during
a reset.

The phy_short_reach sysfs node is now destroyed later in the
port shutdown process, so check for STATE_RUNNING after
acquiring the rtnl_lock (just like in set_phy_flash_cfg).

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>