nl80211: delete interface from bridge before removing the interface

[Yoel D.]

I've encountered the following error during hostapd shutdown process:

    hostapd: nl80211: Failed to remove interface wlan0-1 from bridge
br0: No such device

I think that this error occurs because the function
wpa_driver_nl80211_if_remove() removes the specified interface from
the host via the function nl80211_remove_iface() before deleting it
from the bridge via the function linux_br_del_if().

Thus, when the function linux_br_del_if() is finally invoked in the
next few lines of code, the aforementioned error is raised since the
interface no longer exists.