'struct shutdown_handler' is not modified in this driver.
Constifying this structure moves some data to a read-only section, so
increase overall security.
On a x86_64, with allmodconfig:
Before:
======
text data bss dec hex filename
7043 788 8 7839 1e9f drivers/xen/manage.o
After:
=====
text data bss dec hex filename
7164 676 8 7848 1ea8 drivers/xen/manage.o
Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>