Make swift-recon usable on hosts without IPv6

Fixes a bug when swift-recon --sockstat is used on hosts without
IPv6 support.

Tested by disabling IPv6 on Ubuntu 12.04 LTS:

Add "ipv6.disable=1" to GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub
sudo update-grub
sudo /sbin/reboot

Closes-Bug: 1270711
Change-Id: Ib31a059e412ac68ca0a3faef4201fec7560d1178
Merge "Make swift-recon usable on hosts without IPv6"