Do not write bg_scan_period value if default (-1) has not been changed

There is no need to force this configuration parameter to be written
into the configuration file for each network block that has not modified
the default value.

Signed-hostap: Jouni Malinen <j@w1.fi>

wpa_supplicant/config_file.c

@@ -588,7 +588,7 @@ static void wpa_config_write_network(FILE *f, struct wpa_ssid *ssid)
 	write_psk(f, ssid);
 	write_proto(f, ssid);
 	write_key_mgmt(f, ssid);
-	INT(bg_scan_period);
+	INT_DEF(bg_scan_period, DEFAULT_BG_SCAN_PERIOD);
 	write_pairwise(f, ssid);
 	write_group(f, ssid);
 	write_auth_alg(f, ssid);