mph_send_config_logchpar doesn't update encryption config
In A-bis, the BSC is permitted to change the encryption parameters of an
active logical channel via a "RSL MODE MODIFY" message. osmo-bts-sysmo
doesn't pass along this information to the L1, which is a violation of
OpenBSC seems to only set encryption parameters during channel
activation or during the CIPHERING MODE COMMAND but not modify it later.
However, the code for sending encryption information as part of RSL MODE
MODIFY is implemented in libbsc/abis_rs.lc:rsl_chan_mode_modify_req()