check if active state before stopping pdcp entity

lib/src/upper/pdcp.cc

@@ -53,7 +53,9 @@ void pdcp::init(srsue::rlc_interface_pdcp *rlc_, srsue::rrc_interface_pdcp *rrc_
 void pdcp::stop()
 {
   for(uint32_t i=0;i<SRSLTE_N_RADIO_BEARERS;i++) {
-    pdcp_array[i].stop();
+    if (pdcp_array[i].is_active()) {
+      pdcp_array[i].stop();
+    }
   }
 }