Update git submodules

Update git submodules

* Update docs/submodules/vswitchperf from branch 'master'
  - Merge "ixia: Support of 1 NIC connection to trafficgen"
  - ixia: Support of 1 NIC connection to trafficgen

    For some testcases it is useful to have only one connection between
    traffic generator and DUT. Thus IxNet class was extended to support
    such connection. Feature is enabled if both IXIA ports are set to
    the same value.
    New integration testcase ixnet_pvp_tput_1nic was created to demonstrate
    this feature.
    Unused code was removed from 3rd_party/ixia/ixnetrfc2544.tcl to simplify
    introduction of new features and to speed up IXIA configuration.

    JIRA: VSPERF-503

    Change-Id: I92ab24fa58eeb1ccb7f00ac7f3530ffca7b99241
    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>