Added error display and read/send iteration

[t-nakagawa-esol]

1. The current implementation cannot distinguish between time-outs and other errors for the receive/send function. So, we might have to add a specified number of retries for the other errors below. EAGAIN , EWOULDBLOCK or EINTR for read/send

2. It might not be possible to guarantee that sizeof(frame) will always return in the return value of the read/send function Therefore, it might be necessary to repeat until the size of the return value becomes the sizeof(frame).

3. In the wait function, the current implementation does not distinguish between timeouts and other errors. Therefore, it might be necessary to display errno for errors other than timeout.