API: copy the data to send into the tcp internal buffer (esphome#1455)

Without the flag lwip only holds a reference to the supplied buffers and the reference must be valid until the tcp ack is received. This can't be guaranteed for stack allocated buffers

esphome/components/api/api_connection.cpp

@@ -676,8 +676,10 @@ bool APIConnection::send_buffer(ProtoWriteBuffer buffer, uint32_t message_type)
     }
   }
 
-  this->client_->add(reinterpret_cast<char *>(header.data()), header.size());
-  this->client_->add(reinterpret_cast<char *>(buffer.get_buffer()->data()), buffer.get_buffer()->size());
+  this->client_->add(reinterpret_cast<char *>(header.data()), header.size(),
+                     ASYNC_WRITE_FLAG_COPY | ASYNC_WRITE_FLAG_MORE);
+  this->client_->add(reinterpret_cast<char *>(buffer.get_buffer()->data()), buffer.get_buffer()->size(),
+                     ASYNC_WRITE_FLAG_COPY);
   bool ret = this->client_->send();
   return ret;
 }