Documentation: Document user_events ioctl code

The user events trace subsystem uses the 0x2A/'*' code for ioctls. These
are published via the uapi/linux/user_events.h header file.

Add a line indicating user events as the owner of the 0x2A/'*' code and
reserve the first 32 sequence numbers.

Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240715181413.1157-1-beaub@linux.microsoft.com

Author: beaubelgrave

Documentation/userspace-api/ioctl/ioctl-number.rst

@@ -97,6 +97,8 @@ Code  Seq#    Include File                                           Comments
 '%'   00-0F  include/uapi/linux/stm.h                                System Trace Module subsystem
                                                                      <mailto:alexander.shishkin@linux.intel.com>
 '&'   00-07  drivers/firewire/nosy-user.h
+'*'   00-1F  uapi/linux/user_events.h                                User Events Subsystem
+                                                                     <mailto:linux-trace-kernel@vger.kernel.org>
 '1'   00-1F  linux/timepps.h                                         PPS kit from Ulrich Windl
                                                                      <ftp://ftp.de.kernel.org/pub/linux/daemons/ntp/PPS/>
 '2'   01-04  linux/i2o.h