ovs: Update OVS submodule.

Building the OVS submodule is currently broken for the OVN CI due
to a change in flake8 2.7.0 which introduced the F824 check [0][1].

This was tackled in OVS commit 7f4ee4395637 by disabling the check.

0: PyCQA/flake8#1974
1: PyCQA/pyflakes#825
Signed-off-by: Frode Nordahl <[email protected]>
Acked-by: Ales Musil <[email protected]>
Signed-off-by: Dumitru Ceara <[email protected]>

Author: fnordahl