Update git submodules

* Update docs/submodules/vswitchperf from branch 'master'
  - cleanup: remove fuel plugin since fuel@opnfv uses mcp

    Change-Id: Ibe2028b01c38fa545e72a00a7ef47103d1112b82
    Signed-off-by: Guo Ruijing <ruijing.guo@intel.com>

diff --git a/docs/submodules/vswitchperf b/docs/submodules/vswitchperf
index 6da87d9..16f7eb2 160000 (submodule)
--- a/docs/submodules/vswitchperf
+++ b/docs/submodules/vswitchperf
@@ -1 +1 @@
-Subproject commit 6da87d98f88ac23aa379369d573bbd1a8a1fd7b7
+Subproject commit 16f7eb21ac16ea0f1ba82516a8d4b75c4ede1519