correct way to pass callbacks

Hi,


The bridgestp module needs two callbacks from the bridge when it
attaches which so far I have just passed on with the function call.

bstp_attach(&sc->sc_stp, bridge_state_change, bridge_rtable_expire);

I have always felt this was rather ugly so have attached a patch to put
them both in a struct, is this the right way to do it?

bstp_attach(&sc->sc_stp, &cb);


cheers,
Andrew