code: def gen_veth_str(self, const_str, intf_str):
          
          avl_len = constants.MAX_VETH_NAME - len(const_str)
          if avl_len <= 0:
              LOG.error("veth string name too short")
              raise dfae.DfaAgentFailed(reason="Veth Unavailable")
          start_pos = len(intf_str) - avl_len
          veth_str = const_str + intf_str[start_pos:]
          return veth_str
docs: Generate a veth string.
  
          Concatenates the constant string with remaining available length
          of interface string from trailing position.