IP_STATUS_FILE and routing improvements (#130)

- Obtains VPN public IP address from routing table
- Logs and writes VPN Public IP address to `/ip` as soon as VPN is up
- Obtain port forward, logs it and writes it as soon as VPN is up
- Routing fully refactored and tested
- Routing reads from `/proc/net/route`
- Routing mutates the routes using `ip route ...`

internal/routing/routing.go

@@ -0,0 +1,30 @@
+package routing
+
+import (
+	"net"
+
+	"github.com/qdm12/golibs/command"
+	"github.com/qdm12/golibs/files"
+	"github.com/qdm12/golibs/logging"
+)
+
+type Routing interface {
+	AddRoutesVia(subnets []net.IPNet, defaultGateway net.IP, defaultInterface string) error
+	DefaultRoute() (defaultInterface string, defaultGateway net.IP, defaultSubnet net.IPNet, err error)
+	CurrentPublicIP(defaultInterface string) (ip net.IP, err error)
+}
+
+type routing struct {
+	commander   command.Commander
+	logger      logging.Logger
+	fileManager files.FileManager
+}
+
+// NewConfigurator creates a new Configurator instance
+func NewRouting(logger logging.Logger, fileManager files.FileManager) Routing {
+	return &routing{
+		commander:   command.NewCommander(),
+		logger:      logger.WithPrefix("routing: "),
+		fileManager: fileManager,
+	}
+}