Update git submodules

Update git submodules

* Update docs/submodules/netvirt from branch 'master'
  to 4c40aacd08af1a60b8c3b7b1783178af3bd13fbb
  - NETVIRT-1037: Upstream Fixes --- Review-4

    Introduces a few useful fixes in the VPN Engine.
    Particularly, some of the yang-based flags used during the VPN deletion
    life-cycle are not cleared properly if the deletion fails, leading to
    stale vpn op interface entries.

    Change-Id: I817338174bfda0ea881a066484d944f013138b8e
    Signed-off-by: eupakir <kiran.n.upadhyaya@ericsson.com>
    Signed-off-by: Sam Hague <shague@redhat.com>