CLOCK_MONOTONIC datagram timestamps by the kernel

Hello,

In Linux, it is possible to ask the kernel to timestamp incoming
datagrams when they are received, then to retrieve this timestamp with
an ioctl command.

SIOCGSTAMP
Return a struct timeval with the receive timestamp of the last
packet passed to the user. This is useful for accurate round trip time
measurements. See setitimer(2) for a description of struct timeval.

As far as I understand, this timestamp is given by the CLOCK_REALTIME
clock. I would like to get the timestamp given by a different clock: the
CLOCK_MONOTONIC clock.

In other words, I would like the kernel to do the equivalent of

struct timespec spec;
clock_gettime(CLOCK_MONOTONIC, &spec)

for each datagram the system receives, as soon as it is received.

How can I achieve that?

Is there a different ioctl perhaps? (I don't think so.)