paging: Remove obsolete paging call-back support

The call-back was needed inside the NITB to determine which part (CC,
SMS, ...) had triggered a given paging.   A pure BSC doesn't need that
feature, so let's get rid of it.

The 'void *cbfn_data' is replaced with a 'struct bsc_msc_data *', as
all callers use it with that type.

Change-Id: I8839e8338d3ad1a91b41e687e8412fcdca3fd9ab
4 files changed