EthernetClient::write returns wrong value when buffer size exceeds W5100.SSIZE

[rayshobby]

The return value of EthernetClient::write should be the return value of Ethernet::socketSend:

Ethernet/src/EthernetClient.cpp

Line 86 in 75a3c37

if (Ethernet.socketSend(sockindex, buf, size)) return size;

Otherwise if the buffer to be sent is larger than W5100.SSIZE it will only send W5100.SSIZE number of characters,
https://github.com/arduino-libraries/Ethernet/blob/master/src/socket.cpp#L428
yet EthernetClient::write still returns 'size'.

A better way to implement EthernetClient::write is to add a loop until the whole content is sent.