When wifi is turned off, drv_mac80211_teardown sometimes fails (silently)
because the device to be torn down is not defined.
This situation arises if drv_mac80211_setup was called twice when
wifi was turned on.
This commit ensures that the device to be torn down is always defined
in drv_mac80211_teardown.
Steps to reproduce:
1) Use /sbin/wifi to turn on wifi.
uci set wireless.@wifi-iface[0].disabled=0
uci set wireless.@wifi-device[0].disabled=0
uci commit
wifi
2) Use /sbin/wifi to turn off wifi.
uci set wireless.@wifi-device[0].disabled=1
uci commit
wifi
3) Observe that wifi is still up.
branches affected: trunk, 21.02
Signed-off-by: Bob Cantor <coxede6557@w3boats.com>
d515f6b6cd