MBEDTLS_SSL_CHK_BUF_READ_PTR macro

This macro checks if the remaining length in an input buffer is greater or equal than a needed length. If it is not the case, it returns #MBEDTLS_ERR_SSL_DECODE_ERROR error and pends a #MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR alert message. This is a function-like macro. It is guaranteed to evaluate each argument exactly once.