Routing improvements (#268)

- Fixes #82 
- Remove `EXTRA_SUBNETS`
- Remove no longer needed iptables rules
- Reduce routing interface arity
- Routing setup is done in main.go instead of in the firewall
- Routing setup gets reverted at shutdown

docker-compose.yml

@@ -35,7 +35,4 @@ services:
 
       # Mullvad only
       - COUNTRY=Sweden
-
-      # Allow for example your LAN, set to: 192.168.1.0/24
-      - EXTRA_SUBNETS=
     restart: always