Create default EndpointSettings if no --network provided

Following flags are silently ignored when they're passed with no
`--network` specified (ie. when the default network is used):

- `--network-alias`
- `--ip`
- `--ip6`
- `--link-local-ip`

This is not really an issue right now since the first 3 parameters are
not allowed on the default bridge network. However, with
[moby/moby#45905][1], the container-wide MacAddress parameter will be
deprecated and dismissed. Because of that, with [docker/cli#4419][2],
it's currently not possible to use the `--mac-address` flag with no
default network specified.

Morever, `docker network connect --link-local-ip ...` works properly, so
it should also work on `docker container create`. This also lay the
ground for making the default bridge network just a "normal" network.

Since the 3 parameters in the list above aren't ignored anymore, if
users provide them, moby's ContainerStart endpoint will complain about
those. To provide better UX, [moby/moby#46183][3] make sure these
invalid parameters lead to a proper error message on `docker container
create` / `docker run`.

[1]: https://github.com/moby/moby/pull/45905
[2]: https://github.com/docker/cli/pull/4419
[3]: https://github.com/moby/moby/pull/46183

Signed-off-by: Albin Kerouanton <albinker@gmail.com>

cli/command/container/opts.go

@@ -732,6 +732,20 @@ func parseNetworkOpts(copts *containerOptions) (map[string]*networktypes.Endpoin
 		hasUserDefined, hasNonUserDefined bool
 	)
 
+	if len(copts.netMode.Value()) == 0 {
+		n := opts.NetworkAttachmentOpts{
+			Target: "default",
+		}
+		if err := applyContainerOptions(&n, copts); err != nil {
+			return nil, err
+		}
+		ep, err := parseNetworkAttachmentOpt(n)
+		if err != nil {
+			return nil, err
+		}
+		endpoints["default"] = ep
+	}
+
 	for i, n := range copts.netMode.Value() {
 		n := n
 		if container.NetworkMode(n.Target).IsUserDefined() {
@@ -792,7 +806,7 @@ func applyContainerOptions(n *opts.NetworkAttachmentOpts, copts *containerOption
 		n.Aliases = make([]string, copts.aliases.Len())
 		copy(n.Aliases, copts.aliases.GetAll())
 	}
-	if copts.links.Len() > 0 {
+	if n.Target != "default" && copts.links.Len() > 0 {
 		n.Links = make([]string, copts.links.Len())
 		copy(n.Links, copts.links.GetAll())
 	}