LDAP: extend LDAP systemtap probes of attr list
    
    We would like to see list of requested attributes from LDAP server.
    This patch adds attribute list to probe sdap_search_send where it
    is pretty formated and stored in attrs:string variable.
    
    Content of attrs may for example look like
    
        ["objectClass", "uid", "userPassword", "uidNumber", ...]
    
    Reviewed-by: Michal Židek <mzidek@redhat.com>