selftests/bpf: Use ASSERT_STRNEQ to factor in long slab cache names

subtest_kmem_cache_iter_check_slabinfo() fundamentally compares slab
cache names parsed out from /proc/slabinfo against those stored within
struct kmem_cache_result. The current problem is that the slab cache
name within struct kmem_cache_result is stored within a bounded
fixed-length array (sized to SLAB_NAME_MAX(32)), whereas the name
parsed out from /proc/slabinfo is not. Meaning, using ASSERT_STREQ()
can certainly lead to test failures, particularly when dealing with
slab cache names that are longer than SLAB_NAME_MAX(32)
bytes. Notably, kmem_cache_create() allows callers to create slab
caches with somewhat arbitrarily sized names via its __name identifier
argument, so exceeding the SLAB_NAME_MAX(32) limit that is in place
now can certainly happen.

Make subtest_kmem_cache_iter_check_slabinfo() more reliable by only
checking up to sizeof(struct kmem_cache_result.name) - 1 using
ASSERT_STRNEQ().

Fixes: a496d0cdc84d ("selftests/bpf: Add a test for kmem_cache_iter")
Signed-off-by: Matt Bobrowski <[e-mail]>
Signed-off-by: Martin KaFai Lau <[e-mail]>
Acked-by: Song Liu <[e-mail]>
Link: https://patch.msgid.link/[e-mail]

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

···
 		if (!ASSERT_OK(ret, "kmem_cache_lookup"))
 			break;
 
-		ASSERT_STREQ(r.name, name, "kmem_cache_name");
+		ASSERT_STRNEQ(r.name, name, sizeof(r.name) - 1,
+			      "kmem_cache_name");
 		ASSERT_EQ(r.obj_size, objsize, "kmem_cache_objsize");
 
 		seen++;