The idea behind aux_diag:
- provide generic mechanism to diagnose application connected to WRPC
  via SNMP
- now, it is used to diagnose WR Streamers and later a user can
  define usage of aux_diag
- it can also happen that aux_diag is used for streamers and user-defined
  application

Thus, the following changes were made:
- diag_id=1 is reserved for wr_streamers
- diag_id=0 is reserved for "not used"
- if the input to board is diag_id=0, and streamers are enabled,
  diag_id is 1 and the aux_diag in/out of WRPC is the one of the
  streamers
- if the input to board is diag_id>1, and streamers are enabled,
  diag_id is the input diag_id and the aux_diag in/out of WRPC is
  concatenation of the diag from streamers and input aux_diag
- if the input ot board is diag_id>1, and streamers are disabled,
  diag_id and aux_diag in/out comes from the user