rgw: S3's Browser Upload is handled in incompliantly with the S3 documentation
According to the Browser Uploads to S3 using HTML POST Forms any field after the file is ignored:
file The input field that allows a user to select a file to upload. This field must be the last one in the form, as any fields below it are ignored by S3.
However, RGWPostObj_ObjStore_S3::complete_get_params extracts such fields even if they are placed after the file.