Always include Ports within inspect response

Related to containerd#3310

New behavior will always initialize a NetworkSettings entity within the inspect response.
If the target container does not exist, the NetworkSettings will be full
of "zero-value" members.
If the target container is active, but ports were not published, then
the Ports key of NetworkSettings will have an empty structure value.
If the target container is active and ports were published, then the
Ports key of NetworkSettings will have populated values.

Signed-off-by: Sam Chew <stchew@amazon.com>

pkg/inspecttypes/dockercompat/dockercompat.go

@@ -186,7 +186,7 @@ type ContainerState struct {
 }
 
 type NetworkSettings struct {
-	Ports *nat.PortMap `json:",omitempty"`
+	Ports *nat.PortMap
 	DefaultNetworkSettings
 	Networks map[string]*NetworkEndpointSettings
 }
@@ -398,12 +398,15 @@ func statusFromNative(x containerd.Status, labels map[string]string) string {
 }
 
 func networkSettingsFromNative(n *native.NetNS, sp *specs.Spec) (*NetworkSettings, error) {
-	if n == nil {
-		return nil, nil
-	}
 	res := &NetworkSettings{
 		Networks: make(map[string]*NetworkEndpointSettings),
 	}
+	resPortMap := make(nat.PortMap)
+	res.Ports = &resPortMap
+	if n == nil {
+		return res, nil
+	}
+
 	var primary *NetworkEndpointSettings
 	for _, x := range n.Interfaces {
 		if x.Interface.Flags&net.FlagLoopback != 0 {
@@ -447,8 +450,11 @@ func networkSettingsFromNative(n *native.NetNS, sp *specs.Spec) (*NetworkSetting
 			if err != nil {
 				return nil, err
 			}
-			res.Ports = nports
+			for portLabel, portBindings := range *nports {
+				resPortMap[portLabel] = portBindings
+			}
 		}
+
 		if x.Index == n.PrimaryInterface {
 			primary = nes
 		}