nr pdcp: use pdcp config

There was a problem with SN size. It was hardcoded to 12 bits (so max
sn = 4095) but we configure the UE with 18 bits. After a while, iperf
didn't work anymore because of this (what a surprise!).

So let's get the correct value from pdcp_Config.

And while we're at it, let's store also discard_timer and t_reordering
that will be used later by a proper NR PDCP layer (which is currently
work in progress).

cmake_targets/CMakeLists.txt

@@ -1968,6 +1968,7 @@ set(NR_PDCP_SRC
   ${OPENAIR2_DIR}/LAYER2/nr_pdcp/nr_pdcp_ue_manager.c
   ${OPENAIR2_DIR}/LAYER2/nr_pdcp/nr_pdcp_entity.c
   ${OPENAIR2_DIR}/LAYER2/nr_pdcp/nr_pdcp_entity_drb_am.c
+  ${OPENAIR2_DIR}/LAYER2/nr_pdcp/asn1_utils.c
   )
 
 set(L2_SRC