Update git submodules

* Update docs/submodules/vswitchperf from branch 'master'
  - build: Automated VPP build

    VSPERF makefiles were updated to automatically download and compile
    VPP. VPP will not be installed into the OS, but it will be executed
    from VSPERF's src subdirectory. Thus underlying OS is not affected
    by VPP build required by VSPERF. It also allows quick switch among
    different versions of various tools used by VSPERF.

    As part of this patch, VERIFY and MERGE CI jobs were updated to
    build VPP and test it with basic set of integration tests.

    JIRA: VSPERF-493

    Change-Id: I958b9031c4fefc87c4c63a471d2ba1a0db1eaaa4
    Signed-off-by: Martin Klozik <martinx.klozik@intel.com>
    Reviewed-by: Al Morton <acmorton@att.com>
    Reviewed-by: Christian Trautman <ctrautma@redhat.com>
    Reviewed-by: Sridhar Rao <sridhar.rao@spirent.com>
    Reviewed-by: Trevor Cooper <trevor.cooper@intel.com>

diff --git a/docs/submodules/vswitchperf b/docs/submodules/vswitchperf
index 59aae8c..b878f49 160000 (submodule)
--- a/docs/submodules/vswitchperf
+++ b/docs/submodules/vswitchperf
@@ -1 +1 @@
-Subproject commit 59aae8c0539ca9632d9ffdcb2788ab715fbff9ec
+Subproject commit b878f491b6590678210aa94ed49327d192148144