Move some helper functions into dockertestutil package

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

integration/dockertestutil/config.go

@@ -0,0 +1,28 @@
+package dockertestutil
+
+import "github.com/ory/dockertest/v3/docker"
+
+func DockerRestartPolicy(config *docker.HostConfig) {
+	// set AutoRemove to true so that stopped container goes away by itself on error *immediately*.
+	// when set to false, containers remain until the end of the integration test.
+	config.AutoRemove = false
+	config.RestartPolicy = docker.RestartPolicy{
+		Name: "no",
+	}
+}
+
+func DockerAllowLocalIPv6(config *docker.HostConfig) {
+	if config.Sysctls == nil {
+		config.Sysctls = make(map[string]string, 1)
+	}
+	config.Sysctls["net.ipv6.conf.all.disable_ipv6"] = "0"
+}
+
+func DockerAllowNetworkAdministration(config *docker.HostConfig) {
+	config.CapAdd = append(config.CapAdd, "NET_ADMIN")
+	config.Mounts = append(config.Mounts, docker.HostMount{
+		Type:   "bind",
+		Source: "/dev/net/tun",
+		Target: "/dev/net/tun",
+	})
+}