Please note this documentation is not 100% accurate. This change in behavior was also added into 15.1R6, 16.1R5, 16.2R2, and 15.1X53-D56. Now I believe setting fowarding-options dhcp-security in these releases (as well as 17.1R1+) turns on just dhcp-snooping, and that in any earlier releases I "believe" this knob did nothing, but I am not 100% sure, and have not been able to find a definitive answer.
Just FYI.