Saturate negative memory stat values at '0'.

Docker-DCO-1.1-Signed-off-by: Vishnu Kannan <vishnuk@google.com> (github: vishh)
Merge pull request #201 from vishh/stats_rounding

Saturate negative memory stat values at '0'.
Merge pull request #203 from MalteJ/master

Adding IPv6 network support
Fix leaking file descriptor in NetNs strategy

Docker-DCO-1.1-Signed-off-by: Hugo Duncan <hugo@hugoduncan.org> (github: hugoduncan)
Merge pull request #205 from hugoduncan/fix-leaking-fd-in-netns

Fix leaking file descriptor in NetNs strategy
implementing SetInterfaceMac