Per 8.3.10 of the MQXRTOS RTCS User's Guide, you can define RTCSCFG_LINKOPT_8023 to a '1' to:
"By default, RTCS sends and receives Ethernet II frames. Set this value to 1 (one) to have
RTCS send and receive both Ethernet 802.3 and Ethernet II frames."
There are also two setsockopt() commands, RTCS_SO_LINK_TX_8023 and RTCS_SO_LINK_TX_8023.
How do I use the above options to send/receive Layer 2, 802.3 packets? Where is there some example code?