Minor fixes in trust anchor code

This commit makes some minor changes to the trust anchor code:

1. Replace the undescriptive n1, n2 and n3 identifiers with slightly
   better rdata1, rdata2, and rdata3.
2. Fix an occurrence where in the error log message a static number
   32 was printed, rather than the rdata3 length.
3. Add a default case to the switch statement checking DS digest
   algorithms to catch unknown algorithms.
68 jobs for !2676 with trust-anchors-minor-fixes in 20 minutes and 48 seconds (queued for 7 seconds)
detached
Status Job ID Name Coverage
  Precheck
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