good news: the sum of the three patches you sent solved the problem as far as I have tested yet. Now bat0 works in combination with the bridge and also ethernet traffic is bridged into the mini-mesh setup I use correctly. Furthermore there are no ogm messages visible anymore at bat0 (with the command batctl td bat0).
Do you see a chance to add these changes to the compatibility code for older kernels (I guess for kernels < 2.6.39)?
Thanks for the excellent help, Andreas