openvswitch: bump to version 2.13.0

openvswitch: bump to version 2.13.0

python2 library is now removed as the transition has been done by the
upstream project

OVN is now a separate project released with its own release plan and
it's not included within openvswitch starting with ovs 2.13.

openvswitch.mk is split out from the main Makefile for adding ovn
packages back in following commits.

The following two patches are already included in 2.13

 - ovsdb-idlc-fix-dict-change-during-iteration.patch
 - compat-Include-confirm_neigh-parameter-if-needed.patch

Signed-off-by: Yousong Zhou <redacted>