[ACS44] Cherry pick for CLOUDSTACK-6241

[Sheng Yang]

Hi Daan,

Could you help to cherry pick the following commit to 4.4 branch?

commit d32f5c70d26ce82561bbdce962fd881a644ab81c
Author: Sheng Yang <sheng.y...@citrix.com>
Date:   Fri Mar 14 13:36:43 2014 -0700

    CLOUDSTACK-6241: Fix default route for IPv6 network when IPv4 not used
    (cherry picked from commit e406adc0810b22ded0964080946f019be1337b52)

Thanks!

--Sheng