For the BSC/NITB application we see that people modify the band
without modifying the ARFCN. This creates an unbootable config.
Using the new hook the BSC/NITB can check if the config is
consistent and prevent the config file being written.
Related: SYS#739
If LAPDm receives an I-Frame while there already is an I-Frame in the
tx_queue the code generates an additional RR (to acknowledge the
received I-Frame). Instead, N(R) of the I-Frame in the tx_queue should
be updated to ACK the data.