Update go.mod and go.sum to latest version from networkservicemesh/cm…

…d-nsc-vpp@main

PR link: networkservicemesh/cmd-nsc-vpp#352

Commit: 15e6994
Author: Network Service Mesh Bot
Date: 2022-01-24 22:40:30 -0600
Message:
  - Update go.mod and go.sum to latest version from networkservicemesh/sd…
Signed-off-by: NSMBot <nsmbot@networkservicmesh.io>

apps/nsc-memif/nsc.yaml

@@ -17,7 +17,7 @@ spec:
     spec:
       containers:
         - name: nsc
-          image: ghcr.io/networkservicemesh/ci/cmd-nsc-vpp:b788510
+          image: ghcr.io/networkservicemesh/ci/cmd-nsc-vpp:15e6994
           imagePullPolicy: IfNotPresent
           env:
             - name: SPIFFE_ENDPOINT_SOCKET