Improve cryptic error messages for when a user tries to create_sessio…

…n or destroy_session from a non-owner thread

src/rpc_impl/rpc_sm_api.cc

@@ -18,7 +18,10 @@ int Rpc<TTr>::create_session_st(std::string remote_uri, uint8_t rem_rpc_id) {
 
   // Check that the caller is the creator thread
   if (!in_dispatch()) {
-    ERPC_WARN("%s: Caller thread is not the creator thread.\n", issue_msg);
+    ERPC_WARN(
+        "%s: Cannot create session from a thread other than the one that "
+        "created this erpc::Rpc object.\n",
+        issue_msg);
     return -EPERM;
   }
 
@@ -81,7 +84,10 @@ int Rpc<TTr>::destroy_session_st(int session_num) {
           session_num);
 
   if (!in_dispatch()) {
-    ERPC_WARN("%s: Caller thread is not creator.\n", issue_msg);
+    ERPC_WARN(
+        "%s: Can't destroy session from a thread other than the one that "
+        "created this erpc::Rpc object.\n",
+        issue_msg);
     return -EPERM;
   }