selftests/bpf: add loop test 4

Add a test that returns a 'random' number between [0, 2^20)
If state pruning is not working correctly for loop body the number of
processed insns will be 2^20 * num_of_insns_in_loop_body and the program
will be rejected.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Yonghong Song <yhs@fb.com>

tools/testing/selftests/bpf/prog_tests/bpf_verif_scale.c

@@ -71,6 +71,7 @@ void test_bpf_verif_scale(void)
 
 		{ "loop1.o", BPF_PROG_TYPE_RAW_TRACEPOINT },
 		{ "loop2.o", BPF_PROG_TYPE_RAW_TRACEPOINT },
+		{ "loop4.o", BPF_PROG_TYPE_SCHED_CLS },
 
 		/* partial unroll. 19k insn in a loop.
 		 * Total program size 20.8k insn.