make the logging.Tracer and logging.ConnectionTracer a struct

[marten-seemann]

Fixes #3704.

We’re jumping through a number of hoops here to be able to continue testing using gomock.

[codecov]

Codecov Report

Merging #4082 (5c5d314) into master (ab1c1be) will increase coverage by 0.08%.
The diff coverage is 83.38%.

@@            Coverage Diff             @@
##           master    #4082      +/-   ##
==========================================
+ Coverage   83.59%   83.67%   +0.08%     
==========================================
  Files         148      149       +1     
  Lines       15227    15341     +114     
==========================================
+ Hits        12728    12836     +108     
- Misses       1999     2004       +5     
- Partials      500      501       +1     

Files Changed	Coverage Δ
interface.go	0.00% <ø> (ø)
internal/ackhandler/ackhandler.go	0.00% <ø> (ø)
internal/ackhandler/sent_packet_handler.go	74.50% <0.00%> (-0.58%)	⬇️
internal/handshake/crypto_setup.go	57.73% <0.00%> (ø)
internal/congestion/cubic_sender.go	81.18% <50.00%> (ø)
server.go	76.29% <61.90%> (ø)
logging/connection_tracer.go	89.54% <89.54%> (ø)
connection.go	72.84% <89.74%> (+0.02%)	⬆️
internal/ackhandler/ecn.go	84.47% <90.91%> (ø)
client.go	58.12% <100.00%> (ø)
... and 4 more

... and 1 file with indirect coverage changes