In some situations (a lot of UEs with a lot of traffic), we see
the following crash of the eNB:

Assertion ((UE_id = find_uci(ul_config_pdu->uci_sr_pdu.ue_information.ue_information_rel8.rnti, proc->frame_tx,proc->subframe_tx,eNB,SEARCH_EXIST_OR_FREE))>=0) failed!
In handle_nfapi_ul_pdu() /home/oai-gnb/test1/openairinterface5g/openair1/SCHED/fapi_l1.c:722
No available UE UCI for rnti 5e05

The array uci_vars is too small. If too much UEs have to use PUCCH
at the same time over a few TTIs, we will exhaust the array.

The solution proposed by this commit is to increase the size of this
array. We now make it a matrix and the first dimension is the subframe.

That seems to solve the problem.

A better solution may be found at some point.