tracing: Have memmapped ring buffer use ioctl of "R" range 0x20-2F

To prevent conflicts with other ioctl numbers to allow strace to have an
idea of what is happening, add the range of ioctls for the trace buffer
mapping from _IO("T", 0x1) to the range of "R" 0x20 - 0x2F.

Link: https://lore.kernel.org/linux-trace-kernel/[e-mail]/
Link: https://lore.kernel.org/linux-trace-kernel/[e-mail]/

Cc: Jonathan Corbet <[e-mail]>
Fixes: cf9f0f7c4c5bb ("tracing: Allow user-space mapping of the ring-buffer")
Link: https://lore.kernel.org/[e-mail]
Reported-by: "Dmitry V. Levin" <[e-mail]>
Reviewed-by: Mathieu Desnoyers <[e-mail]>
Acked-by: Masami Hiramatsu (Google) <[e-mail]>
Signed-off-by: Steven Rostedt (Google) <[e-mail]>

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

···
 'Q'   all    linux/soundcard.h
 'R'   00-1F  linux/random.h                                          conflict!
 'R'   01     linux/rfkill.h                                          conflict!
+'R'   20-2F  linux/trace_mmap.h
 'R'   C0-DF  net/bluetooth/rfcomm.h
 'R'   E0     uapi/linux/fsl_mc.h
 'S'   all    linux/cdrom.h                                           conflict!

include/uapi/linux/trace_mmap.h

···
 	__u64	Reserved2;
 };
 
-#define TRACE_MMAP_IOCTL_GET_READER		_IO('T', 0x1)
+#define TRACE_MMAP_IOCTL_GET_READER		_IO('R', 0x20)
 
 #endif /* _TRACE_MMAP_H_ */