Enable additional linters and fix reported issues

[Danielius1922]

No description provided.

[codecov-commenter]

Codecov Report

Merging #339 (47597fc) into master (75000ae) will increase coverage by 0.01%.
The diff coverage is 40.00%.

@@            Coverage Diff             @@
##           master     #339      +/-   ##
==========================================
+ Coverage   69.54%   69.55%   +0.01%     
==========================================
  Files          67       67              
  Lines        5618     5617       -1     
==========================================
  Hits         3907     3907              
  Misses       1303     1303              
+ Partials      408      407       -1     

Impacted Files	Coverage Δ
net/dtlslistener.go	70.00% <ø> (ø)
server.go	0.00% <0.00%> (ø)
tcp/server.go	81.28% <ø> (ø)
tcp/session.go	70.85% <0.00%> (ø)
udp/client.go	84.74% <ø> (ø)
udp/discover.go	54.54% <ø> (ø)
udp/server.go	83.01% <0.00%> (ø)
tcp/clientconn.go	68.19% <20.00%> (-0.12%)	⬇️
net/blockwise/blockwise.go	67.58% <40.00%> (ø)
message/getETag.go	61.53% <50.00%> (ø)
... and 5 more

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