Update git submodules

Update git submodules

* Update docs/submodules/yardstick from branch 'master'
  - Merge "Add send socket commands function"
  - Add send socket commands function

    Pktgen provides a TCP socket connection to allow the user to control
    it from a remote console or program [1].

    This new method will provide Yardstick the ability to send string
    commands to a port in a remote host.

    [1] http://pktgen-dpdk.readthedocs.io/en/latest/socket.html

    JIRA: YARDSTICK-1186

    Change-Id: I9d64ccad662fa3599de65654c5dab02833fcc91d
    Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>