Update git submodules

Update git submodules

* Update docs/submodules/sfc from branch 'master'
  - Harmonize vxlan-tool calls

    Renamed vxlan_firewall and vxlan_tool_stop to start_vxlan_tool and
    stop_vxlan_tool respectively. Added some comments to explain their
    behavior.

    Cleaned both functions to use ".format()" string formatting, which
    improves readability.

    Modified behavior of start_vxlan_tool: now it does NOT block
    traffic by default

    Change-Id: I6754b020a474be1e9adf2d83e7c9f5053930b702
    Signed-off-by: Juan Vidal <juan.vidal.allende@ericsson.com>