move most of cni/pkg to plugins/pkg: delete code staying in cni/pkg

This moves the following packages to this repository:
* ip
* ipam
* ns
* testutils
* utils

plugins/meta/tuning/tuning.go

@@ -24,11 +24,11 @@ import (
 	"path/filepath"
 	"strings"
 
-	"github.com/containernetworking/cni/pkg/ns"
 	"github.com/containernetworking/cni/pkg/skel"
 	"github.com/containernetworking/cni/pkg/types"
 	"github.com/containernetworking/cni/pkg/types/current"
 	"github.com/containernetworking/cni/pkg/version"
+	"github.com/containernetworking/plugins/pkg/ns"
 )
 
 // TuningConf represents the network tuning configuration.