chardev: replace qemu_set_nonblock()

Those calls are either for non-socket fd, or are POSIX-specific. Use the
dedicated GLib API. (qemu_set_nonblock() is for socket-like)

(this is a preliminary patch before renaming qemu_set_nonblock())

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
diff --git a/chardev/char-fd.c b/chardev/char-fd.c
index 6ec9682..cf78454 100644
--- a/chardev/char-fd.c
+++ b/chardev/char-fd.c
@@ -212,8 +212,8 @@
     FDChardev *s = FD_CHARDEV(chr);
     g_autofree char *name = NULL;
 
-    if (fd_out >= 0) {
-        qemu_set_nonblock(fd_out);
+    if (fd_out >= 0 && !g_unix_set_fd_nonblocking(fd_out, true, NULL)) {
+        assert(!"Failed to set FD nonblocking");
     }
 
     if (fd_out == fd_in && fd_in >= 0) {