Update git submodules

* Update docs/submodules/vswitchperf from branch 'stable/euphrates'
  - conf: Fix default VPP configuration

    Number of VPP workers (aka PMD threads) was not specified
    explicitly in default configuration file. Configuration
    has been fixed to use the same cores as OVS with DPDK.

    Change-Id: Icd3e5d6f429435fbc1ff580891f4b182d1c48729
    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>
    (cherry picked from commit e1080a507901f7b957f24c75170594b4f9bc9740)

diff --git a/docs/submodules/vswitchperf b/docs/submodules/vswitchperf
index 0638a09..55429d9 160000 (submodule)
--- a/docs/submodules/vswitchperf
+++ b/docs/submodules/vswitchperf
@@ -1 +1 @@
-Subproject commit 0638a091d2a6fa7d4d98f7659a816ac1c67162c0
+Subproject commit 55429d9203032fe7b5dd9ac81cec81cec4e4a17d