Add comment explaining why cancel is not called in success path after client transport is created
Add comment explaining why cancel is not called in success path after client transport is created

fuchsia-mirror/third_party-grpc-grpc-go,stanley-cheung/grpc-go,MakMukhi/grpc-go,stanley-cheung/grpc-go,andreimatei/grpc-go,peter-edge/grpc-go,dfawley/grpc-go,MakMukhi/grpc-go,rakyll/grpc-go,dfawley/grpc-go,rakyll/grpc-go,fuchsia-mirror/third_party-grpc-grpc-go,grpc/grpc-go,menghanl/grpc-go,improbable-io/grpc-go,andreimatei/grpc-go,menghanl/grpc-go,thinkerou/grpc-go,peter-edge/grpc-go,improbable-io/grpc-go,grpc/grpc-go,thinkerou/grpc-go