int32 need to be changed to uint32

[erenliu168]

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Bug description

As above, there are some fields in both http and tcp connection pool in DestinationRule which value default to 2^32-1，but the field type is int32。Maybe type of those fields should be changed to uint32 ?

The file is here:
https://github.com/istio/api/blob/master/networking/v1alpha3/destination_rule.pb.go

Affected product area (please put an X in all that apply)

[ ] Configuration Infrastructure
[ ] Docs
[ ] Installation
[X ] Networking
[ ] Performance and Scalability
[ ] Policies and Telemetry
[ ] Security
[ ] Test and Release
[ ] User Experience

Expected behavior
change the type of relative fields to uint32
Steps to reproduce the bug

Version (include the output of istioctl version --remote and kubectl version)

How was Istio installed?

Environment where bug was observed (cloud vendor, OS, etc)

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the dump file to this issue.