rgw/sfs: refactor of SFSBucket::merge_and_store_attrs()

Refactored with a set_and_store_attrs semantics.
The previous implementation was started as if the method should implement a merge but the actual usage suggests set semantics.
The new implementation is more concise and simplified.

Fixes: https://github.com/aquarist-labs/s3gw/issues/798
Signed-off-by: Giuseppe Baccini <giuseppe.baccini@suse.com>

src/rgw/driver/sfs/bucket.cc

@@ -404,21 +404,11 @@ int SFSBucket::
 int SFSBucket::merge_and_store_attrs(
     const DoutPrefixProvider* /*dpp*/, Attrs& new_attrs, optional_yield /*y*/
 ) {
-  for (auto& it : new_attrs) {
-    attrs[it.first] = it.second;
-
-    if (it.first == RGW_ATTR_ACL) {
-      auto lval = it.second.cbegin();
-      acls.decode(lval);
-    }
-  }
-  for (auto& it : attrs) {
-    auto it_find = new_attrs.find(it.first);
-    if (it_find == new_attrs.end()) {
-      // this is an old attr that is not defined in the new_attrs
-      // delete it
-      attrs.erase(it.first);
-    }
+  attrs = new_attrs;
+  auto it = attrs.end();
+  if ((it = attrs.find(RGW_ATTR_ACL)) != attrs.end()) {
+    auto lval = it->second.cbegin();
+    acls.decode(lval);
   }
 
   sfs::get_meta_buckets(get_store().db_conn)