fff-gateway: Use return for errors in config version check

The concept of configuregateway is to respond on the return codes
of the gateway.d files, and exit if anyone returns something different
than zero.

Thus, let's not exit in gateway.d files directly, but stick to that
logic and return 1.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Reviewed-by: Robert Langhammer <rlanghammer@web.de>
Reviewed-by: Fabian Bläse <fabian@blaese.de>

src/packages/fff/fff-gateway/files/etc/gateway.d/01-version

@@ -3,7 +3,7 @@ configure() {
 	if ! uci -q show gateway > /dev/null; then
 		echo "ERROR: Gateway config could not be parsed or does not exist."
 
-		exit 1
+		return 1
 	fi
 
 	# check version of configuration
@@ -13,14 +13,14 @@ configure() {
 	if ! [ -n "$config_version" ]; then
 		echo "ERROR: No config version given. Supported versions: '$expected_version'"
 
-		exit 1
+		return 1
 	fi
 
 	if [ "$config_version" != "$expected_version" ]; then
 		echo "ERROR: Invalid config version. Expected '$expected_version', got '$config_version'."
 		echo "Please check what has been changed and adjust your config appropriately."
 
-		exit 1
+		return 1
 	fi
 
 	return 0