python: Fix lxc-ls's usage of get_ips()

The recent port of get_ips() from pure python to the C API came with
a couple of API changes for that function call (as were highlighted in
the commit message).

I somehow didn't notice that lxc-ls was still calling with the old API
and so was crashing whenever it was asked to show the ipv4 or ipv6 address.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>