A request of given type ('request', default is 0), equipped
with the given 'data', is sent to the erq. If 'callback' is
set to a closure, it will be called when the response from the
erq arrives, if the response carries enough data to work on
void <closure>(int * response_data, int len)
The data given to send_erq() may be either a string, or an
array of integers, which are then interpreted as characters.
The various requests are defined in /sys/erq.h.
The result returned is 0 on failure, or non-zero on success.
The function causes a privilege violation "erq".