Mod: update the comments in protocol directory

[zouyx]

What this PR does:

• update the comments in protocol directory

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[codecov-commenter]

Codecov Report

Merging #602 into develop will decrease coverage by 0.06%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           develop     #602      +/-   ##
===========================================
- Coverage    67.20%   67.14%   -0.07%     
===========================================
  Files          190      190              
  Lines         9918     9918              
===========================================
- Hits          6665     6659       -6     
- Misses        2596     2603       +7     
+ Partials       657      656       -1     

Impacted Files	Coverage Δ
protocol/dubbo/client.go	67.87% <ø> (ø)
protocol/dubbo/codec.go	72.50% <ø> (-5.00%)	⬇️
protocol/dubbo/config.go	13.15% <ø> (ø)
protocol/dubbo/dubbo_protocol.go	91.83% <ø> (ø)
protocol/dubbo/listener.go	57.52% <0.00%> (ø)
protocol/grpc/client.go	61.70% <ø> (ø)
protocol/grpc/grpc_exporter.go	100.00% <ø> (ø)
protocol/grpc/grpc_invoker.go	70.96% <0.00%> (ø)
protocol/grpc/grpc_protocol.go	95.23% <ø> (ø)
protocol/grpc/server.go	68.42% <ø> (ø)
... and 20 more

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[fangyincheng]

LGTM