@azrdev DAVdroid was never able to use SNI on Android < 4.2. In a certain version, there was a severe DAVdroid bug that accepted all certificates – maybe you have tried exactly this version although it wasn’t online very long.
You have more choices, see http://davdroid.bitfire.at/faq/entry/sni-support
Either put all host names into the certificate’s subjectAltName or mount your DAV service into the default HTTPS virtual host so that there’s no need for SNI. You may also use IP- or port-based virtual SSL hosts.
Personally, I recommend to use CyanogenMod or another open-source version of Android in any case. In the course of this, you can also get a newer Android version (>= 4.2) for many devices.