fix(esp_modem): linux port to work with lwip-2.1.2

components/esp_modem/src/esp_modem_primitives_linux.cpp

@@ -89,4 +89,9 @@ void Task::Relinquish()
     usleep(0);
 }
 
-} // namespace esp_modem
+void Task::Delay(uint32_t ms)
+{
+    usleep(ms*1000);
+}
+
+} // namespace esp_modem