Initially these assertions were added to protected simultaneous
send/recv from the same socket when similarly purposed mutexes were
removed.
However, simultaneous send/recv can still be useful for UDP if the
payload is guaranteed to be less than the MTU across the entire
connection.
nsapi_error_t - enum of errors or 0 for NSAPI_ERROR_OK
nsapi_size_t - unsigned size of data that could be sent
nsapi_size_or_error_t - either a non-negative size or negative error
Martin Kojtal
Christopher Haster