mac80211: fix detecting existing interface

Instead of using the actual interface name, a hard-coded 'wlan0' has
slipped into the script. Replace it.

Fixes: ccf2aa9d4b ("mac80211: detect existing interface before adding")
Reported-by: John Crispin <john@phrozen.org>
Signed-off-by: Daniel Golle <daniel@makrotopia.org>

package/kernel/mac80211/files/lib/netifd/wireless/mac80211.sh

@@ -455,7 +455,7 @@ mac80211_iw_interface_add() {
 	[ "$rc" = 233 ] && {
 		# Keep matching pre-existing interface
 		[ -d "/sys/class/ieee80211/${phy}/device/net/${ifname}" ] && \
-		case "$(iw dev wlan0 info | grep "^\ttype" | cut -d' ' -f2- 2>/dev/null)" in
+		case "$(iw dev $ifname info | grep "^\ttype" | cut -d' ' -f2- 2>/dev/null)" in
 			"AP")
 				[ "$type" = "__ap" ] && rc=0
 				;;