Update git submodules

* Update docs/submodules/samplevnf from branch 'stable/fraser'
  - Get multiple port stats simultaneously

    JIRA: YARDSTICK-1220

    Implemented new "multi port stats <port list>" command, which returns a
    semi-colon-separated list of comma-separated values:
    - port id
    - total (at last_tsc) for rx_pkts, tx_pkts, no_mbufs, ierrors + imissed
    - last_tsc

    Change-Id: I8a8da79cb4ccb245ccb38b50b561da51a40a359d
    Signed-off-by: Patrice Buriez <patrice.buriez@intel.com>
    (cherry picked from commit a9d9979b1f5b7435552ae884da69220a42b81f81)
    Signed-off-by: Emma Foley <emma.l.foley@intel.com>

diff --git a/docs/submodules/samplevnf b/docs/submodules/samplevnf
index 95e9ab8..56abe2d 160000 (submodule)
--- a/docs/submodules/samplevnf
+++ b/docs/submodules/samplevnf
@@ -1 +1 @@
-Subproject commit 95e9ab89f6d8f9911a9fdb625e8721f3d2e20b1a
+Subproject commit 56abe2d0604c519a911b91ec43e87889a2990361