I looked at the source code and it seems that CM already has the 3G fixes needed to make HC radio work.
You are missing one 3G specific file: /system/lib/libsec-ril.so
And a few lines in build.prop:
I added these to your p6800 rom, but it still doesn't work. It looks like it thinks it's a wifi only tablet.
Unfortunately i have a slow PC and i don't have that much time to try and build it myself.
HTC One X (Stock Android 4.0.4)
Samsung Galaxy Nexus (Stock Android 4.2)
LG Nexus 4 (Stock Android 4.2)
Asus Nexus 7 (Stock Android 4.2)
Samsung Galaxy Tab 7.7 3G (Stock Android 4.0.4)
Samsung Galaxy Tab 8.9 3G (Android 4.1.2 AOSP ROM)