p2p: use a bool for send()

Identified by @selsta

Callers can otherwise misinterpret int -1 as truthy success,
e.g. see make_payload_send_txs

(cherry picked from commit 9bf193728bb11beb9c40e06a0d48d1c697fe7a84)

contrib/epee/include/net/levin_protocol_handler_async.h

@@ -106,7 +106,7 @@ public:
   template<class callback_t>
   int invoke_async(int command, message_writer in_msg, boost::uuids::uuid connection_id, const callback_t &cb, size_t timeout = LEVIN_DEFAULT_TIMEOUT_PRECONFIGURED);
 
-  int send(epee::byte_slice message, const boost::uuids::uuid& connection_id);
+  bool send(epee::byte_slice message, const boost::uuids::uuid& connection_id);
   bool close(boost::uuids::uuid connection_id, const bool wait_for_shutdown);
   bool update_connection_context(const t_connection_context& contxt);
   bool request_callback(boost::uuids::uuid connection_id);
@@ -743,8 +743,8 @@ public:
       `message_writer::finalize_notify`. See additional instructions for
       `make_fragmented_notify`.
 
-      \return 1 on success */
-  int send(byte_slice message)
+      \return true on success */
+  bool send(byte_slice message)
   {
     const misc_utils::auto_scope_leave_caller scope_exit_handler = misc_utils::create_scope_leave_handler(
       boost::bind(&async_protocol_handler::finish_outer_call, this)
@@ -753,9 +753,9 @@ public:
     if (!send_message(std::move(message)))
     {
       LOG_ERROR_CC(m_connection_context, "Failed to send message, dropping it");
-      return -1;
+      return false;
     }
-    return 1;
+    return true;
   }
   //------------------------------------------------------------------------------------------
   boost::uuids::uuid get_connection_id() {return m_connection_context.m_connection_id;}
@@ -935,11 +935,11 @@ void async_protocol_handler_config<t_connection_context>::set_handler(levin_comm
 }
 //------------------------------------------------------------------------------------------
 template<class t_connection_context>
-int async_protocol_handler_config<t_connection_context>::send(byte_slice message, const boost::uuids::uuid& connection_id)
+bool async_protocol_handler_config<t_connection_context>::send(byte_slice message, const boost::uuids::uuid& connection_id)
 {
   async_protocol_handler<t_connection_context>* aph;
   int r = find_and_lock_connection(connection_id, aph);
-  return LEVIN_OK == r ? aph->send(std::move(message)) : 0;
+  return LEVIN_OK == r ? aph->send(std::move(message)) : false;
 }
 //------------------------------------------------------------------------------------------
 template<class t_connection_context>

contrib/epee/include/storages/levin_abstract_invoke2.h

@@ -138,10 +138,10 @@ namespace epee
       levin::message_writer to_send;
       stg.store_to_binary(to_send.buffer);
 
-      int res = transport.send(to_send.finalize_notify(command), conn_id);
-      if(res <=0 )
+      bool res = transport.send(to_send.finalize_notify(command), conn_id);
+      if(!res)
       {
-        MERROR("Failed to notify command " << command << " return code " << res);
+        MERROR("Failed to notify command " << command);
         return false;
       }
       return true;