epoll: Stop spin between TCP connect and received data
epoll: Stop spin between TCP connect and received data

If a client TCP connection connects, EPOLLOUT remains enabled so epoll_wait()
always returns immediately causing a loop until there is other data traffic.

This fix is to enable EPOLLIN and disable EPOLLOUT if COAP_SOCKET_WANT_WRITE
is not set at point of connection successful.

authmillenon/libcoap,authmillenon/libcoap,authmillenon/libcoap