It is the path to the host mkdir, not to the target mkdir. Just use
/bin/mkdir.
-e 's|@includedir[@]|$(includedir)|g' \
-e 's|@exec_prefix[@]|$(exec_prefix)|g' \
-e 's|@prefix[@]|$(prefix)|g' \
- -e 's|@mkdir_p[@]|$(mkdir_p)|g' \
-e 's|@VERSION[@]|$(VERSION)|g' \
-e 's|@PACKAGE[@]|$(PACKAGE)|g' \
-e 's|@PACKAGE_NAME[@]|$(PACKAGE_NAME)|g' \
NotifyAccess=main
EnvironmentFile=-/etc/default/lldpd
EnvironmentFile=-/etc/sysconfig/lldpd
-ExecStartPre=@mkdir_p@ @PRIVSEP_CHROOT@
+ExecStartPre=/bin/mkdir @PRIVSEP_CHROOT@
ExecStart=@sbindir@/lldpd $DAEMON_ARGS $LLDPD_OPTIONS
Restart=on-failure
PrivateTmp=yes