I think this is not the best way to do so. IMHO, you should write your own MAC code using RIOT’s code guidelines, API, stacks and common best practices.
Semtech’s code appears in different coding style and implements different approaches in implementation so it wouldn’t fit in RIOT’s code well without full re-writing.
the "RIOT way" or rather the GNRC way would be to extend (in the
object oriented sense) `gnrc_netdev2_t`, similar how
`gnrc_netdev2_ieee80215.c` and `gnrc_netdev2_eth.c` already did. Hope
I was able to helpful.