qemu-char: add qemu_chr_disconnect to close a fd accepted by listen fd

The patch introduces qemu_chr_disconnect(). The function is used for
closing a fd accepted by listen fd. Though we already have qemu_chr_delete(),
but it closes not only accepted fd but also listen fd. This new function
is used when we still want to keep listen fd.

Signed-off-by: Tetsuya Mukawa <mukawa@igel.co.jp>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Tested-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Reviewed-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Reviewed-by: Victor Kaplansky <victork@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
diff --git a/qemu-char.c b/qemu-char.c
index b13ecbb..e312777 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -4012,6 +4012,13 @@
     s->avail_connections++;
 }
 
+void qemu_chr_disconnect(CharDriverState *chr)
+{
+    if (chr->chr_disconnect) {
+        chr->chr_disconnect(chr);
+    }
+}
+
 static void qemu_chr_free_common(CharDriverState *chr)
 {
     g_free(chr->filename);
@@ -4389,6 +4396,7 @@
     chr->chr_write = tcp_chr_write;
     chr->chr_sync_read = tcp_chr_sync_read;
     chr->chr_close = tcp_chr_close;
+    chr->chr_disconnect = tcp_chr_disconnect;
     chr->get_msgfds = tcp_get_msgfds;
     chr->set_msgfds = tcp_set_msgfds;
     chr->chr_add_client = tcp_chr_add_client;