mac80211: do not drop tx nulldata packets on encrypted links

ieee80211_tx_h_select_key drops any non-mgmt packets without a key when
encryption is used. This is wrong for nulldata packets that can't be
encrypted and are sent out for probing clients and indicating 4-address
mode.
Reported-by: Sebastian Gottschall <s.gottschall@dd-wrt.com>
Fixes: a0761a30 ("mac80211: drop data frames without key on encrypted links")
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20201218191525.1168-1-nbd@nbd.nameSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/tx.c

@@ -649,7 +649,7 @@ ieee80211_tx_h_select_key(struct ieee80211_tx_data *tx)
 		if (!skip_hw && tx->key &&
 		    tx->key->flags & KEY_FLAG_UPLOADED_TO_HARDWARE)
 			info->control.hw_key = &tx->key->conf;
-	} else if (!ieee80211_is_mgmt(hdr->frame_control) && tx->sta &&
+	} else if (ieee80211_is_data_present(hdr->frame_control) && tx->sta &&
 		   test_sta_flag(tx->sta, WLAN_STA_USES_ENCRYPTION)) {
 		return TX_DROP;
 	}