/etc/network/interfaces/br0:
auto br0
iface br0 inet static
  bridge_ports wlan0
  address 192.168.0.30
  netmask 255.255.255.0
  gateway 192.168.0.1
  wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf

/etc/network/interfaces/wlan0:
iface wlan0 inet manual