[9.18] Merge branch '3113-clientinfo-refactor' into 'main'

Instead of using an extra rarely-used paramater to dns_clientinfo_init() to set ECS information for a client, this commit adds a function dns_clientinfo_setecs() which can be called only when ECS is needed.

(cherry picked from commit ff3fdaa4)

Backport of MR !5782 (merged)