can't add interfaces to bridge

[Steve Franks]

I'm getting the following error - ifconfig: BRDGADD ath0: Invalid argument

Given the following commands (which work for my tap interface with
qemu on 7.1, but apparently not with two regular network cards on
6.3):

sudo kldload if_bridge
sudo ifconfig ath0 down
sudo ifconfig rl0 down
sudo ifconfig bridge0 destroy
sudo ifconfig bridge0 create
sudo ifconfig bridge0 addm ath0
sudo ifconfig bridge0 addm rl0
sudo ifconfig bridge0 up
sudo ifconfig ath0 up
sudo ifconfig rl0 up
sudo dhclient bridge0
ifconfig

I get the following output:

[steve at aire /usr/home/steve]$ bridge
kldload: can't load if_bridge: File exists
net.link.tap.user_open: 1 -> 1
net.link.tap.devfs_cloning: 1 -> 1
net.link.tap.up_on_open: 1 -> 1
ifconfig: BRDGADD ath0: Invalid argument
ifconfig: BRDGADD rl0: Invalid argument
DHCPDISCOVER on bridge0 to 255.255.255.255 port 67 interval 8
ath0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        inet 192.168.2.69 netmask 0xffffff00 broadcast 192.168.2.255
        ether 00:13:f7:4a:0f:a8
        media: IEEE 802.11 Wireless Ethernet autoselect (DS/1Mbps)
        status: no carrier
        ssid "" channel 3
        authmode OPEN privacy ON deftxkey 1 wepkey 1:104-bit txpowmax 39
        bmiss 7 protmode CTS burst bintval 100
rl0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        options=8<VLAN_MTU>
        inet 192.168.1.1 netmask 0xffffff00 broadcast 192.168.1.255
        ether 00:01:6c:16:44:6f
        media: Ethernet autoselect (none)
        status: no carrier
plip0: flags=108810<POINTOPOINT,SIMPLEX,MULTICAST,NEEDSGIANT> mtu 1500
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
        inet6 fe80::1%lo0 prefixlen 64 scopeid 0x4
        inet6 ::1 prefixlen 128
        inet 127.0.0.1 netmask 0xff000000
bridge0: flags=8802<BROADCAST,SIMPLEX,MULTICAST> mtu 1500
        ether ea:57:36:3c:28:0c
        priority 32768 hellotime 2 fwddelay 15 maxage 20
[steve at aire /usr/home/steve]$

Thanks,
Steve