tracing: Rename trace_array field max_buffer to snapshot_buffer

tracing: Rename trace_array field max_buffer to snapshot_buffer

When tracing was first added, there were latency tracers that would take a
snapshot of the current trace when a new max latency was hit. This
snapshot buffer was called "max_buffer". Since then, a snapshot feature
was added that allowed user space or event triggers to trigger a snapshot
of the current buffer using the same max_buffer of the trace_array.

As this snapshot buffer now has a more generic use case, calling it
"max_buffer" is confusing. Rename it to snapshot_buffer.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: https://patch.msgid.link/20260208183856.428446729@kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>