Supporting SI2quater as per 3GPP TS 44.018 will require chnages to the
way System Information is stored because it uses 1:n instead of 1:1
mapping between SI type and generated SI content. This should not affect
other SI types though. To facilitate this transition:
* convert the code to always use GSM_BTS_SI helper instead of accessing
buffer directly
* make helper more robust by adding extra parenthesis
* add similar helper for gsm_lchan
* add function estimating number of SI2quater message to hold configured
number of (U|E)ARFCNs
* add SI2q index/count fields and pass them to rest_octets generator
explicitly
* internalize buffer access in generate_si* functions
Change-Id: I74e4e3cb86364cec869a1472a41b4a95af0d50dd
Related: RT#8792
000d9b61a8