nl80211: Fix SIGNAL_POLL in IBSS and mesh

NL80211_CMD_GET_STATION does not work with the IBSS/mesh BSSID, so clear
the signal strength instead of returning failure when SIGNAL_POLL is
used in an IBSS/mesh.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>

src/drivers/driver_nl80211.c

@@ -6560,8 +6560,12 @@ static int nl80211_signal_poll(void *priv, struct wpa_signal_info *si)
 
 	os_memset(si, 0, sizeof(*si));
 	res = nl80211_get_link_signal(drv, si);
-	if (res != 0)
-		return res;
+	if (res) {
+		if (drv->nlmode != NL80211_IFTYPE_ADHOC &&
+		    drv->nlmode != NL80211_IFTYPE_MESH_POINT)
+			return res;
+		si->current_signal = 0;
+	}
 
 	res = nl80211_get_channel_width(drv, si);
 	if (res != 0)