tools: replace add with xadd (#3518)

resolve #3481
replace add with xadd for more tools.
diff --git a/tools/zfsdist.py b/tools/zfsdist.py
index 112b10c..a30671d 100755
--- a/tools/zfsdist.py
+++ b/tools/zfsdist.py
@@ -98,7 +98,7 @@
     // store as histogram
     dist_key_t key = {.slot = bpf_log2l(delta)};
     __builtin_memcpy(&key.op, op, sizeof(key.op));
-    dist.increment(key);
+    dist.atomic_increment(key);
 
     start.delete(&tid);
     return 0;