For kernel contributions to the ieee802514 and 6lowpan subsystems we follow the usual kernel development approach. In a nutshell you would write a patch, send it to the development mailing list via git send-email, wait for review and feedback, re-spin if necessary and wait for the patch to be applied to one of our git trees.
We run two different git trees. One for bugfixes which should go directly into the current kernel in development (we also consider stable backports if marked accordingly), wpan.
The second git tree is for new features and bigger developments that are scheduled for the next merge window, wpan-next.
All patches should be send to email@example.com.
If in doubt, do not worry to much about all the details, send your contribution and we will figure out together where to put it. :-)