bpf: verifier: reorder stack size check with dead code sanitization

Reorder the calls to check_max_stack_depth() and sanitize_dead_code()
to separate functions which can rewrite instructions from pure checks.

No functional changes.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Jiong Wang <jiong.wang@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

kernel/bpf/verifier.c

@@ -6983,10 +6983,11 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr,
 	free_states(env);
 
 	if (ret == 0)
-		sanitize_dead_code(env);
+		ret = check_max_stack_depth(env);
 
+	/* instruction rewrites happen after this point */
 	if (ret == 0)
-		ret = check_max_stack_depth(env);
+		sanitize_dead_code(env);
 
 	if (ret == 0)
 		/* program is valid, convert *(u32*)(ctx + off) accesses */