Use Go canonical import paths

Add canonical imports only in existing doc.go files.
https://golang.org/doc/go1.4#canonicalimports

Fixes #29014

pkg/registry/networkpolicy/doc.go

@@ -14,4 +14,4 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-package networkpolicy
+package networkpolicy // import "k8s.io/kubernetes/pkg/registry/networkpolicy"