DoH: Use trace_id() in logging to differentiate between connections

As multiple connections on the same netId can exist at the same
time, use trace_id() to differentiate between them.

Also, upgrade timer logging message from trace level to debug level.

Bug: 215818810
Test: built dnsresolver pass
Change-Id: Idacb8310c9b1b66551abf8b12216b1be2db1705e