[PATCH] $selected was not properly reinitialized in dialup_admin

Hello. I'm sending this patch to fix a small bug in dialup_admin. This was making weird behavior when a user was member of multiple groups. The $selected array should be reinitialized on each iteration of i to avoid more than one "selected" operator in the dropdown. -- Octavio. Twitter: @alvarezp2000 -- Identi.ca: @alvarezp