mac80211: fix IBSS/adhoc mode for brcmfmac

On systems using brmcfmac (e.g. Raspberry Pi Zero W) without this fix,
the final setup-call:
iw dev wlan0 ibss join ...

fails with returncode 161 and message:
"command failed: Not supported (-95)"

So this patch calls an explicit:
iw dev wlan0 set type ibss
just prior to the 'ibss join' command.

I have tested several ath9k and mt76xx devices
with different revisions: this patch does not harm.

please also apply to stable branch.

Signed-off-by: Bastian Bittorf <bb@npl.de>
(cherry-picked from commit ea5fce3f46)

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

@@ -861,6 +861,7 @@ mac80211_setup_adhoc() {
 	mcval=
 	[ -n "$mcast_rate" ] && wpa_supplicant_add_rate mcval "$mcast_rate"
 
+	iw dev "$ifname" set type ibss
 	iw dev "$ifname" ibss join "$ssid" $freq $iw_htmode fixed-freq $bssid \
 		beacon-interval $beacon_int \
 		${brstr:+basic-rates $brstr} \