um: Do not propagate noreboot parameter to kernel

This parameter is UML specific and is unknown to kernel. It should not
be propagated to kernel, otherwise it could be passed to user space as
a command line option by kernel with a warning like:

Unknown kernel command line parameters "noreboot", will be passed to user space.

Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20241011040441.1586345-6-tiwei.btw@antgroup.com


Signed-off-by: Johannes Berg <johannes.berg@intel.com>