code: func (*endpoint) Capabilities() stack.LinkEndpointCapabilities {
  	return stack.CapabilityRXChecksumOffload | stack.CapabilityTXChecksumOffload | stack.CapabilitySaveRestore | stack.CapabilityLoopback
  }
docs: // Capabilities implements stack.LinkEndpoint.Capabilities. Loopback advertises
  // itself as supporting checksum offload, but in reality it's just omitted.