Use the RX_SECIDX_* enums in more places

Add symbols for security indices 1 (old-stlye auth2, unused) and
2 (rxkad with always-encrypt, maybe-used).

Use the global symbols instead of custom defines like BULK_NULL and
SAMPLE_NULL.

Change-Id: I82bbb0016a5c3129dfd18ff7dc77ff7839501ad8
auditU: also report for rxkad-always-encrypt

The logic that works for security index 2 also works for index 3.

Change-Id: Ifd868fa8d9d0ba2f422fa1fac43e4f583d27a1ff
rx: Named values for securityObjectStats types

Stop using hardcoded constances and use defined symbols for these
values.

Change-Id: I3edcf809572cb8c8360af19dcab7a12c4d1be4a9