rootless: support `podman network create` (CNI-in-slirp4netns)

Usage:
```
$ podman network create foo
$ podman run -d --name web --hostname web --network foo nginx:alpine
$ podman run --rm --network foo alpine wget -O - http://web.dns.podman
Connecting to web.dns.podman (10.88.4.6:80)
...
<h1>Welcome to nginx!</h1>
...
```

See contrib/rootless-cni-infra for the design.

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

1 files changed, 4 insertions, 0 deletions

diff --git a/libpod/networking_unsupported.go b/libpod/networking_unsupported.go
index dd72a3fd8..76bb01424 100644
--- a/libpod/networking_unsupported.go
+++ b/libpod/networking_unsupported.go
@@ -8,6 +8,10 @@ func (r *Runtime) setupRootlessNetNS(ctr *Container) error {
 	return define.ErrNotImplemented
 }
 
+func (r *Runtime) setupSlirp4netns(ctr *Container) error {
+	return define.ErrNotImplemented
+}
+
 func (r *Runtime) setupNetNS(ctr *Container) error {
 	return define.ErrNotImplemented
 }