test: fix race reading while incrementing (#2935)
test: fix race reading while incrementing (#2935)

Swap the `<-done` and `if numConns < 2` to make sure `numConns++` happens before read
dfawley/grpc-go,menghanl/grpc-go,dfawley/grpc-go,stanley-cheung/grpc-go,grpc/grpc-go,menghanl/grpc-go,grpc/grpc-go,stanley-cheung/grpc-go