MINOR: cli: add mworker_accept_wrapper to 'show fd'

In the output of 'show fd', the worker CLI's socketpair was still
handled by an "unknown" function. That can be really confusing during
debug. Fixed it by showing "mworker_accept_wrapper" instead.
diff --git a/src/cli.c b/src/cli.c
index 4356586..ef58ba6 100644
--- a/src/cli.c
+++ b/src/cli.c
@@ -921,6 +921,7 @@
 			     (fdt.iocb == dgram_fd_handler) ? "dgram_fd_handler" :
 			     (fdt.iocb == listener_accept)  ? "listener_accept" :
 			     (fdt.iocb == poller_pipe_io_handler) ? "poller_pipe_io_handler" :
+			     (fdt.iocb == mworker_accept_wrapper) ? "mworker_accept_wrapper" :
 			     "unknown");
 
 		if (fdt.iocb == conn_fd_handler) {