Multiple IP addresses: add them in the correct order

Make sure that when configuring containers that have interfaces containing
multiple IP addresses they are added in the order of the configuration file
(i.e. the first being the primary one) and not the reverse order.

Signed-off-by: Christian Seiler <christian@iwakd.de>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>