run the internal and http3 tests with race detector on Travis

[marten-seemann]

Depends on #2380.

[codecov-io]

Codecov Report

Merging #2385 into master will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2385      +/-   ##
==========================================
- Coverage   86.15%   86.13%   -0.02%     
==========================================
  Files         122      122              
  Lines        9542     9681     +139     
==========================================
+ Hits         8220     8338     +118     
- Misses        984      995      +11     
- Partials      338      348      +10     

Impacted Files	Coverage Δ
internal/ackhandler/sent_packet_handler.go	74.33% <0.00%> (+3.48%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 4d83009...b128ad5. Read the comment docs.

[marten-seemann]

@lucas-clemente Please have another look. I had to make a lot of changes to this PR.
Note the trick using go:linkname in the handshake tests to access unexported functions in the qtls package without any external dependencies.