tracing: start net/trace span in ChildSpan

[tbg]

Fixes #16881.

[cockroach-teamcity]

This change is 

[RaduBerinde]

LGTM, thanks for the fix!

[RaduBerinde]

Review status: 0 of 1 files reviewed at latest revision, 1 unresolved discussion, some commit checks pending.

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pkg/util/tracing/tracer.go, line 347 at r1 (raw file):

	}

	if pSpan.netTr != nil {

[nit] conceptually, this belongs right after the shadowTr check (they're both "backends" in a way)

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Comments from Reviewable

[RaduBerinde]

pkg/util/tracing/tracer.go, line 347 at r1 (raw file):

Previously, RaduBerinde wrote…

[nit] conceptually, this belongs right after the shadowTr check (they're both "backends" in a way)

ah but I see StartSpan does the same, so disregard

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Comments from Reviewable