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, 0 insertions, 11 deletions

diff --git a/libpod/container_validate.go b/libpod/container_validate.go
index d657e3549..b78168cd1 100644
--- a/libpod/container_validate.go
+++ b/libpod/container_validate.go
@@ -2,7 +2,6 @@ package libpod
 
 import (
 	"github.com/containers/podman/v2/libpod/define"
-	"github.com/containers/podman/v2/pkg/rootless"
 	spec "github.com/opencontainers/runtime-spec/specs-go"
 	"github.com/pkg/errors"
 )
@@ -68,16 +67,6 @@ func (c *Container) validate() error {
 		}
 	}
 
-	// Rootless has some requirements, compared to networks.
-	if rootless.IsRootless() {
-		if len(c.config.Networks) > 0 {
-			return errors.Wrapf(define.ErrInvalidArg, "cannot join CNI networks if running rootless")
-		}
-
-		// TODO: Should we make sure network mode is set to Slirp if set
-		// at all?
-	}
-
 	// Can only set static IP or MAC is creating a network namespace.
 	if !c.config.CreateNetNS && (c.config.StaticIP != nil || c.config.StaticMAC != nil) {
 		return errors.Wrapf(define.ErrInvalidArg, "cannot set static IP or MAC address if not creating a network namespace")