pkg/multus: skip GetAsVersion conversion when cniVersion is already 1.x

@gemini-code-assist suggestion on k8snetworkplumbingwg#1505: emptyCNIResult already
returns a *cni100.Result, so GetAsVersion is a no-op (or worse, an
unnecessary allocation) for 1.x configs. Gate the conversion on
non-1.x cniVersions only; 1.x callers now return the *cni100.Result
directly as they did before the panic fix.

Behaviour for 0.3.x / 0.4.0 is unchanged: still downcast so skel's
conversion chain dispatches convertFrom04x correctly.

Signed-off-by: SAY-5 <SAY-5@users.noreply.github.com>

Author: SAY-5

pkg/multus/multus.go

@@ -768,12 +768,13 @@ func CmdAdd(args *skel.CmdArgs, exec invoke.Exec, kubeClient *k8s.ClientInfo) (c
 		if stderrors.Is(err, errPodNotFound) {
 			emptyResult := emptyCNIResult(args, n.CNIVersion)
 			logging.Verbosef("CmdAdd: Warning: pod [%s/%s] not found, exiting with empty CNI result: %v", k8sArgs.K8S_POD_NAMESPACE, k8sArgs.K8S_POD_NAME, emptyResult)
-			// Downcast to the types package matching n.CNIVersion so skel's
-			// response conversion path calls the right convertFrom*/To*
-			// converter. Returning a *cni100.Result with CNIVersion 0.3.1
-			// trips convertFrom04x's type assertion to *types040.Result
-			// and panics (#1497).
-			if n.CNIVersion != "" {
+			// emptyCNIResult already returns a *cni100.Result, so 1.x
+			// configs don't need conversion. For older cniVersions
+			// (0.3.x / 0.4.0) we must downcast so skel's response
+			// conversion path calls the right convertFrom*/To* converter;
+			// otherwise convertFrom04x's type assertion to *types040.Result
+			// panics (#1497).
+			if n.CNIVersion != "" && !strings.HasPrefix(n.CNIVersion, "1.") {
 				versioned, convErr := emptyResult.GetAsVersion(n.CNIVersion)
 				if convErr != nil {
 					return nil, cmdErr(k8sArgs, "failed to downcast empty CNI result to cniVersion %q: %v", n.CNIVersion, convErr)