Yes. If you already have the security license then you have that feature enabled.... unfortunately 2921 doesn't have the free users for ssl. You have to add the license to get SSL VPN....
For 10 users, 25 users, 100 users like that.... 2921 can have max of 100 users....
FL-SSLVPN10-K9(=), FL-SSLVPN25-K9(=), and FL-SSLVPN100-K9(=) depends on your user count and requirement.
To run SSL VPN, you would need both securityK9 and SSL VPN license.