Hi…
Just a quick update on this... I managed to do it with bridging another interface with my LAN interface and setting R-STP on switches...
At first it was not working, because you indeed have to add pf rules also to bridged interface, to allow traffic, which makes no sense networking wise, but, nevermind, it works at the end.
The problem arised with VLAN-s. No way to make it work. Not with bridged interface, then I created VLAN with same id on bridged interface, still nothing, then I bridged VLAN-s with same ID on both interfaces together, nothing...
So I gave up for now...
/jan