The tool descriptions have always advertised kernel_datapath as a
requestable field, but the handler's whitelist did not contain it: asking
for it was rejected as an invalid field, so the MCP clients could not see
which links run on kernel interfaces at all.
Also record what seeding a netem experiment on IOU costs: IOL emits its own
CDP/keepalive frames and they draw from the netem RNG stream, so a
seeded run only reproduces after `no cdp run` (verified bit-identical pcaps).