Update git submodules

Update git submodules

* Update docs/submodules/vswitchperf from branch 'master'
  - Merge "vswitches/ovs: delete bridges on stop"
  - vswitches/ovs: delete bridges on stop

    On stop, remove all created bridges in order to clean the working
    environment.

    Moreover, when an OVS bridge is deleted, remove also all attached ports.

    By the way, as the context manager of OFBridge is never used by the
    current test implementation and by any OVS vswitches in order to manage
    their creation/deletion, let's remove this dead code.

    JIRA: VSPERF-570

    Change-Id: I7ce62d56a8a2fe7b45e693f3c2dd91e1b435567c
    Signed-off-by: Julien Meunier <julien.meunier@6wind.com>