move common code file in common directory

remove several unused files
remove mem_block_t that is never used in a different way than a simple heap buffer
move up IP address type and remove duplications of the same struct declaration

openair2/F1AP/f1ap_cu_task.c

@@ -123,7 +123,6 @@ void *F1AP_CU_task(void *arg) {
   int         result;
   LOG_I(F1AP, "Starting F1AP at CU\n");
   // no RLC in CU, initialize mem pool for PDCP
-  pool_buffer_init();
   itti_mark_task_ready(TASK_CU_F1);
   eth_params_t *IPaddrs;