[kolla][centos][rdo] NOTICE: OVS version mismatch between Wallaby and later

Dears, This is a notice to users of OVS with Kolla with CentOS-Stream-8-based images or RDO directly. It seems that RDO Wallaby currently installs OVS 2.17 while later ones install OVS 2.15. The problem is that currently: *** Upgrades from Wallaby to Xena will cause OVS to misbehave and lose all network connectivity until host reboot. *** This is because downgrades of running OVS are not supported. We are investigating this issue, please stay tuned to this topic. The solution we believe to be the correct one now is to bump OVS to 2.17 also in later branches of RDO. Kind regards, Radek -yoctozepto