net: usb: qmi_wwan: allow qmimux add/del with master up

There's no reason for preventing the creation and removal
of qmimux network interfaces when the underlying interface
is up.

This makes qmi_wwan mux implementation more similar to the
rmnet one, simplifying userspace management of the same
logical interfaces.

Fixes: c6adf779 ("net: usb: qmi_wwan: add qmap mux protocol support")
Reported-by: NAleksander Morgado <aleksander@aleksander.es>
Signed-off-by: NDaniele Palmas <dnlplm@gmail.com>
Acked-by: NBjørn Mork <bjorn@mork.no>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/usb/qmi_wwan.c

@@ -429,13 +429,6 @@ static ssize_t add_mux_store(struct device *d,  struct device_attribute *attr, c
 		goto err;
 	}
 
-	/* we don't want to modify a running netdev */
-	if (netif_running(dev->net)) {
-		netdev_err(dev->net, "Cannot change a running device\n");
-		ret = -EBUSY;
-		goto err;
-	}
-
 	ret = qmimux_register_device(dev->net, mux_id);
 	if (!ret) {
 		info->flags |= QMI_WWAN_FLAG_MUX;
@@ -465,13 +458,6 @@ static ssize_t del_mux_store(struct device *d,  struct device_attribute *attr, c
 	if (!rtnl_trylock())
 		return restart_syscall();
 
-	/* we don't want to modify a running netdev */
-	if (netif_running(dev->net)) {
-		netdev_err(dev->net, "Cannot change a running device\n");
-		ret = -EBUSY;
-		goto err;
-	}
-
 	del_dev = qmimux_find_dev(dev, mux_id);
 	if (!del_dev) {
 		netdev_err(dev->net, "mux_id not present\n");