Testing this with foreman discovery iso 3.6 and 3.6.4.
It appears that booting off the discovery iso does startup lldapd.service and the lldapd.socket but the udev rule 82-enable-lldap, which should trigger for each interface on the system, never runs.
# cat /etc/udev/rules.d/82-enable-lldp.rules
ACTION=="add", SUBSYSTEM=="net", NAME!="lo", TAG+="systemd", ENV{SYSTEMD_WANTS}="enable-lldp@%k.service"
So I never see any lldp facts show up on the discovered host since it is never turned on for the interfaces.
What is also odd is the 83-enable-promiscuous-rules-mode.rules seems to startup for each device just fine.