ovs: Update the submodule to v3.4.2.

It's better to point to the official release tag.  Beside other small
fixes, this bump includes the fix for ct_tp_src/dst extraction for
later fragments in the userspace datapath.

Signed-off-by: Ilya Maximets <[email protected]>
Signed-off-by: Mark Michelson <[email protected]>

Author: igsilya