macsec: let the administrator set UP state even if lowerdev is down

Currently, the kernel doesn't let the administrator set a macsec device
up unless its lower device is currently up. This is inconsistent, as a
macsec device that is up won't automatically go down when its lower
device goes down.

Now that linkstate propagation works, there's really no reason for this
limitation, so let's remove it.

Fixes: c09440f7 ("macsec: introduce IEEE 802.1AE driver")
Reported-by: NRadu Rendec <radu.rendec@gmail.com>
Signed-off-by: NSabrina Dubroca <sd@queasysnail.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/macsec.c

@@ -2812,9 +2812,6 @@ static int macsec_dev_open(struct net_device *dev)
 	struct net_device *real_dev = macsec->real_dev;
 	int err;
 
-	if (!(real_dev->flags & IFF_UP))
-		return -ENETDOWN;
-
 	err = dev_uc_add(real_dev, dev->dev_addr);
 	if (err < 0)
 		return err;