Add READ_READY support to file-system session

The read-ready packet informs the server that the client wants to be
notified if a handle becomes readable. When becoming readable, the
server acknowledges packet and the client may queue a read requests
accordingly.

repos/os/src/server/lx_fs/main.cc

@@ -77,6 +77,10 @@ class File_system::Session_component : public Session_rpc_object
 			case Packet_descriptor::WRITE:
 				res_length = node.write((char const *)content, length, offset);
 				break;
+
+			case Packet_descriptor::READ_READY:
+				/* not supported */
+				break;
 			}
 
 			packet.length(res_length);