Bug#1099191: debian-installer: scanning the mirror stalls frequently

[Kentaro HAYASHI <kenhys@xdump.org>]

Control: severity -1 normal

I've got that when installing Debian with bridge mode with WiFi
interface on Virtualbox guest,
IPv6 connectivity was broken unexpectedly.
    
This bug was well-known and not fixed for a long time.
    
  Bridge mode with WiFi interface: IPv6 does not work via router
  https://www.virtualbox.org//ticket/22153

So, changed severity to normal.

(When using installer on VM, it might affect to tester/developer)
  
Regards,