freq_list should be space separated instead of comma.

Otherwise, wpa_supplicant only reads up to the comma, and in our case,
this meant 5180 (channel 36).

Resolves b/31061434

Change-Id: I0f5677a9c9f46f1112ed1e18b1dd168bd6f0cd08
diff --git a/wifi/configs.py b/wifi/configs.py
index 743fe10..97a27ce 100644
--- a/wifi/configs.py
+++ b/wifi/configs.py
@@ -375,7 +375,7 @@
                                utils.validate_and_sanitize_bssid(opt.bssid))
   network_block = make_network_block(network_block_lines)
 
-  freq_list = ','.join(autochannel.get_all_frequencies(opt.band))
+  freq_list = ' '.join(autochannel.get_all_frequencies(opt.band))
 
   lines = [
       'ctrl_interface=/var/run/wpa_supplicant',