WaitingFor returns "port not found" if NetworkMode == host

[Bablzz]

Describe the bug
WaitingFor returns "port not found" if NetworkMode == host

To Reproduce

func TestContainerWithHostNetworkOptionsAndWaitStrategy(t *testing.T) {
	ctx := context.Background()
	gcr := GenericContainerRequest{ContainerRequest: ContainerRequest{
		Image:       "nginx",
		SkipReaper:  true,
		NetworkMode: "host",
		WaitingFor: wait.ForListeningPort("80/tcp"),
	},
		Started: true,
	}

	nginxC, err := GenericContainer(ctx, gcr)
	if err != nil {
		t.Fatal(err)
	}

	defer nginxC.Terminate(ctx)

	host, err := nginxC.Host(ctx)
	if err != nil {
		t.Errorf("Expected host %s. Got '%d'.", host, err)
	}

	_, err = http.Get("http://" + host + ":80")
	if err != nil {
		t.Errorf("Expected OK response. Got '%d'.", err)
	}
}

Expected behavior
Port found

docker info

Client:
 Debug Mode: false

Server:
 Containers: 2
  Running: 2
  Paused: 0
  Stopped: 18
 Images: 35
 Server Version: 19.03.3
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Native Overlay Diff: true
 Logging Driver: json-file
 Cgroup Driver: cgroupfs
 Plugins:
  Volume: local
  Network: bridge host overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
 Swarm: inactive
 Runtimes: runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: b34a5c8af56e510852c35414db4c1f4fa6172339
 runc version: 3e425f80a8c931f88e6d94a8c831b9d5aa481657
 init version: fec3683
 Security Options:
  apparmor
  seccomp
   Profile: default
 Kernel Version: 5.3.0-29-generic
 Operating System: Ubuntu 19.10
 OSType: linux
 Architecture: x86_64
 CPUs: 8
 Total Memory: 15.34GiB
 Name: 
 ID: 
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 Registry: https://index.docker.io/v1/
 Labels:
 Experimental: false
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false

Additional context
In my mind problem in docker.go

func (c *DockerContainer) MappedPort(ctx context.Context, port nat.Port) (nat.Port, error) 

[Bablzz]

#151

[gianarb]

Fixed