Update git submodules

Update git submodules

* Update docs/submodules/netvirt from branch 'master'
  to a4aa988c5e3d95cc2baf5a0eef12b1d741ab856c
  - statemanager: document the unused dependencies

    StateManager appears to have a number of service dependencies which it
    doesn’t use; but its whole point is to signify that the set of
    services it depends on is ready, as a proxy for the system as a whole
    being ready. This patch suppresses unused warnings.

    Change-Id: I2777d89381ea9a02321645afe45d166a33ff21ad
    Signed-off-by: Stephen Kitt <skitt@redhat.com>