wifi: mac80211: restore non-chanctx injection behaviour

During the transition to use channel contexts throughout, the
ability to do injection while in monitor mode concurrent with
another interface was lost, since the (virtual) monitor won't
have a chanctx assigned in this scenario.

It's harder to fix drivers that actually transitioned to using
channel contexts themselves, such as mt76, but it's easy to do
those that are (still) just using the emulation. Do that.

Cc: stable@vger.kernel.org
Link: https://bugzilla.kernel.org/show_bug.cgi?id=218763
Reported-and-tested-by: Oscar Alfonso Diaz <oscar.alfonso.diaz@gmail.com>
Fixes: 0a44dfc ("wifi: mac80211: simplify non-chanctx drivers")
Link: https://patch.msgid.link/20251216105242.18366-2-johannes@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Author: jmberg-intel

net/mac80211/tx.c

@@ -2397,6 +2397,8 @@ netdev_tx_t ieee80211_monitor_start_xmit(struct sk_buff *skb,
 
 	if (chanctx_conf)
 		chandef = &chanctx_conf->def;
+	else if (local->emulate_chanctx)
+		chandef = &local->hw.conf.chandef;
 	else
 		goto fail_rcu;