remove default value for 'blocking' param from pdcp::write_sdu()

there were two defaults and one was shadowing the other. This
commit removes both defaults and uses blocking-mode for RRC
calls to PDCP in the UE. The eNB write_sdu() uses the non-blocking
mode by default. We have to review the eNB's RRC perhaps and use blocking
there too and non-blocking only for data plane

lib/include/srslte/interfaces/ue_interfaces.h

@@ -221,7 +221,7 @@ public:
   virtual void reestablish()                                                                     = 0;
   virtual void reestablish(uint32_t lcid)                                                        = 0;
   virtual void reset()                                                                           = 0;
-  virtual void write_sdu(uint32_t lcid, srslte::unique_byte_buffer_t sdu, bool blocking = false) = 0;
+  virtual void write_sdu(uint32_t lcid, srslte::unique_byte_buffer_t sdu, bool blocking)         = 0;
   virtual void add_bearer(uint32_t lcid, srslte::pdcp_config_t cnfg)                             = 0;
   virtual void change_lcid(uint32_t old_lcid, uint32_t new_lcid)                                 = 0;
   virtual void config_security(uint32_t                            lcid,

lib/include/srslte/upper/pdcp.h

@@ -44,7 +44,7 @@ public:
   void reestablish();
   void reestablish(uint32_t lcid);
   void reset();
-  void write_sdu(uint32_t lcid, unique_byte_buffer_t sdu, bool blocking = true);
+  void write_sdu(uint32_t lcid, unique_byte_buffer_t sdu, bool blocking);
   void write_sdu_mch(uint32_t lcid, unique_byte_buffer_t sdu);
   void add_bearer(uint32_t lcid, pdcp_config_t cnfg);
   void add_bearer_mrb(uint32_t lcid, pdcp_config_t cnfg);

srsenb/src/stack/upper/pdcp.cc

@@ -165,7 +165,8 @@ void pdcp::write_sdu(uint16_t rnti, uint32_t lcid, srslte::unique_byte_buffer_t
   pthread_rwlock_rdlock(&rwlock);
   if (users.count(rnti)) {
     if (rnti != SRSLTE_MRNTI) {
-      users[rnti].pdcp->write_sdu(lcid, std::move(sdu));
+      // TODO: expose blocking mode as function param
+      users[rnti].pdcp->write_sdu(lcid, std::move(sdu), false);
     } else {
       users[rnti].pdcp->write_sdu_mch(lcid, std::move(sdu));
     }

srsue/src/stack/rrc/rrc.cc

@@ -1716,7 +1716,7 @@ void rrc::send_ul_dcch_msg(uint32_t lcid, const asn1::rrc::ul_dcch_msg_s& msg)
 
   log_rrc_message(get_rb_name(lcid).c_str(), Tx, pdcp_buf.get(), msg, msg.msg.c1().type().to_string());
 
-  pdcp->write_sdu(lcid, std::move(pdcp_buf));
+  pdcp->write_sdu(lcid, std::move(pdcp_buf), true);
 }
 
 void rrc::write_sdu(srslte::unique_byte_buffer_t sdu)