Some trace2 events that lacked def_param have learned to show it,
enriching the output.

Reviewed-by: Josh Steadmon <steadmon@google.com>
cf. <ZejkVOVQBZhLVfHW@google.com>

* jh/trace2-missing-def-param-fix:
  trace2: emit 'def_param' set with 'cmd_name' event
  trace2: avoid emitting 'def_param' set more than once
  t0211: demonstrate missing 'def_param' events for certain commands