No sign of LACP in 6.5U1, only the balancing algorithms

Am setting up a vSAN cluster with vSphere 6.5U1, with Mellanox 100Gb network switches and a distributed vSwitch. The switches support multi-chassis LAG and I've followed the manual to configure it, but for the life of me I cannot find the option to enable LACP in the vCenter or vSphere web UI. I even resorted to the Flash client(!), but still nothing.

The distributed port groups have the appropriate drop-down lists for configuring the balancing algorithm for teaming, but there's no sign of anything to actually enable LACP by that name. I have to set the aggregation group to "on" (static) on the switches to have the MLAG come up, as "active" (LACP) it just sits there marked inactive.

Am I missing something really bloody obvious in the UI? Or is it just not there now and I've done everything right by setting a static aggregation with IP source hash balancing? The appropriate NIC drivers (Mellanox ConnectX4 50Gb NICs) are installed and everything appears correct from that side.