net: phylink: split link_an_mode configured and current settings

Split link_an_mode between the configured setting and the current
operating setting.  This is an important distinction to make when we
need to configure PHY mode for a plugged SFP+ module that does not
use in-band signalling.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>