Part of unforking our winipcfg-go and using upstream (#760), move our
additions into our repo. (We might upstream them later if upstream has
interest)
Originally these were:
@apenwarr: "Add ifc.SyncAddresses() and SyncRoutes()."
609dcf2df5
@bradfitz: "winipcfg: make Interface.AddRoutes do as much as possible, return combined error"
e9f93d53f3
@bradfitz: "prevent unnecessary Interface.SyncAddresses work; normalize IPNets in deltaNets"
decb9ee8e1
