rgw: parse tenant name out of rgwx-bucket-instance

used by multisite bucket full sync to request the listing of a specific
bucket instance. if the bucket lives under a tenant, we need to get that
out of the rgwx-bucket-instance header, because the http request path
only names the bucket

Fixes: https://tracker.ceph.com/issues/50785

Signed-off-by: Casey Bodley <cbodley@redhat.com>

src/rgw/rgw_op.cc

@@ -528,8 +528,8 @@ int rgw_build_bucket_policies(const DoutPrefixProvider *dpp, rgw::sal::Store* st
 
   string bi = s->info.args.get(RGW_SYS_PARAM_PREFIX "bucket-instance");
   if (!bi.empty()) {
-    string bucket_name;
-    ret = rgw_bucket_parse_bucket_instance(bi, &bucket_name, &s->bucket_instance_id, &s->bucket_instance_shard_id);
+    // note: overwrites s->bucket_name, may include a tenant/
+    ret = rgw_bucket_parse_bucket_instance(bi, &s->bucket_name, &s->bucket_instance_id, &s->bucket_instance_shard_id);
     if (ret < 0) {
       return ret;
     }