kernel/utsname_sysctl.c: Add missing enum uts_proc value

bfca3dd3 added new struct ctl_table uts_kern_table[], but not new
enum uts_proc value. It broke the notification mechanism between the
sethostname syscall and the pollers of /proc/sys/kernel/hostname.

The table uts_kern_table is addressed within uts_proc_notify by the enum
value, that's why new enum value is needed.

Fixes: bfca3dd3

 ("kernel/utsname_sysctl.c: print kernel arch")
Reported-by: Torsten Hilbrich <torsten.hilbrich@secunet.com>
Signed-off-by: Petr Vorel <pvorel@suse.cz>
Link: https://lore.kernel.org/r/20221020150645.11719-1-pvorel@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>