netlink: add default Route to NetworkGetRoutes

Docker-DCO-1.1-Signed-off-by: Johan Euphrosine <proppy@google.com> (github: proppy)
network: exclude default routes from checkRouteOverlaps

Docker-DCO-1.1-Signed-off-by: Johan Euphrosine <proppy@google.com> (github: proppy)
netlink: move Route type to common arch file

Docker-DCO-1.1-Signed-off-by: Johan Euphrosine <proppy@google.com> (github: proppy)
netlink: make darwin happy

Docker-DCO-1.1-Signed-off-by: Johan Euphrosine <proppy@google.com> (github: proppy)
Merge pull request #3640 from proppy/networkgetroutes-add-default

netlink: add default Route to NetworkGetRoutes