selftest/bpf/benchs: Print less if the quiet option is set

The bench utility will print

    Setting up benchmark '<bench-name>'...
    Benchmark '<bench-name>' started.

on startup to stdout. Suppress this output if --quiet option if given. This
makes it simpler to parse benchmark output by a script.
Signed-off-by: Anton Protopopov <aspsk@isovalent.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230213091519.1202813-7-aspsk@isovalent.com

tools/testing/selftests/bpf/bench.c

@@ -577,6 +577,7 @@ static void setup_benchmark(void)
 {
 	int i, err;
 
+	if (!env.quiet)
 		printf("Setting up benchmark '%s'...\n", bench->name);
 
 	state.producers = calloc(env.producer_cnt, sizeof(*state.producers));
@@ -623,6 +624,7 @@ static void setup_benchmark(void)
 					    next_cpu(&env.prod_cpus));
 	}
 
+	if (!env.quiet)
 		printf("Benchmark '%s' started.\n", bench->name);
 }