increase default tx_queue length for RLC UM and AM

- With the current default tx queue length (16 SDUs) the BSR reported by the UE
  is too low if the size of the SDU is relativly small (e.g. 100 B).
  This effectivly causes the eNB to only allocate a small grant
  to the UE and thus reduces the UL throughput for small SDUs.

lib/include/srslte/upper/rlc_am.h

@@ -69,7 +69,7 @@ struct rlc_amd_retx_t{
 class rlc_am : public rlc_common
 {
 public:
-  rlc_am(uint32_t queue_len = 16);
+  rlc_am(uint32_t queue_len = 128);
   ~rlc_am();
   void init(log                   *log_,
             uint32_t              lcid_,

lib/include/srslte/upper/rlc_um.h

@@ -48,7 +48,7 @@ class rlc_um
     :public rlc_common
 {
 public:
-  rlc_um(uint32_t queue_len = 32);
+  rlc_um(uint32_t queue_len = 128);
   ~rlc_um();
   void init(log                       *rlc_entity_log_,
             uint32_t                   lcid_,