Code maintenance: Unix abstraction interface

- Used for creating the tun device if it does not exist
- Mocks generated for testing

internal/unix/unix.go

@@ -0,0 +1,24 @@
+package unix
+
+import sysunix "golang.org/x/sys/unix"
+
+//go:generate mockgen -destination=mock_$GOPACKAGE/$GOFILE . Unix
+
+type Unix interface {
+	Mkdev(major uint32, minor uint32) uint64
+	Mknod(path string, mode uint32, dev int) (err error)
+}
+
+func New() Unix {
+	return &unix{}
+}
+
+type unix struct{}
+
+func (u *unix) Mkdev(major uint32, minor uint32) uint64 {
+	return sysunix.Mkdev(major, minor)
+}
+
+func (u *unix) Mknod(path string, mode uint32, dev int) (err error) {
+	return sysunix.Mknod(path, mode, dev)
+}