Add tcpip.Route.String and tcpip.AddressMask.Prefix
Add tcpip.Route.String and tcpip.AddressMask.Prefix

PiperOrigin-RevId: 264544163

google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor