Comment 39 for bug 37120

Thanks, kbang.

Your solution worked for me, modified slightly as I'm using WEP:

iface ra0 inet dhcp
        pre-up ifconfig ra0 up
        pre-up ifconfig ra0 down
        pre-up ifconfig ra0 up
        pre-up ifconfig ra0 down
        pre-up iwconfig ra0 essid "MyRouterName"
        pre-up iwconfig ra0 key "MyKeyInHex"
        pre-up iwconfig ra0 mode Managed
        pre-up ifconfig ra0 up
auto ra0

Now I have wireless connectivity which survives a reboot.