phylink: ensure we take the link down when phylink_stop() is called

[ Upstream commit 2012b7d6b2868c532f22d9172c8b24611637eb48 ]

Ensure that we tell the MAC to take the link down when phylink_stop()
is called, and that this completes prior to phylink_stop() returns.

Reported-by: Florian Fainelli <f.fainelli@gmail.com>
Tested-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>