Prior to this commit, the RAN function for KPM is leaking memory: it
allocates using calloc() but never frees it.

The fix consists of not allocating this memory on the heap in the first
place, but on the stack. Therefore, there are changes to pass in a
pointer to various functions to the structure on the stack, instead of
passing the "container" for the heap memory by value.

Further, the MAC was allocating an excessive amount of memory (N times
sizeof(NR_UE_info_t)). Instead of copying the entire struct, the present
code stores a pointer to the MAC UE container (NR_UE_info_t *). For the
RRC, there is a similar simplification that consists in not storing the
entire struct f1_ue_data_t (which is not required), but only the RRC UE
ID.

Note that both MAC and RRC might suffer from race conditions. For the
MAC, we should lock the scheduler for the time we read statistics. For
the RRC, the problem is more delicate as no mutex exists; the RRC
assumes everything is executed synchronously in the ITTI task loop. In
both cases, this commit does not address this problem