Limit the range from 0 to (_MAX_SYSINFO_TYPE - 1) instead of
0 to 31. This way we will never access the lchan->si.buf[] out
of bounds. This is only a theoretical issue though as the code
filling the lchan->si.buf for the SACCH will not have valid
>= _MAX_SYSINFO_TYPE. Add a small regression test to check we
still schedule all SIs.
Fixes: CID 1040765
Holger Hans Peter Freyther