Simplify byteorder transformation & remove magic number in Authz

[tacslon]

What type of PR is this? /kind enhancement

What this PR does / why we need it:

1. Clarify byteorder transformation in Authz
2. Remove magic number in Authz Which issue(s) this PR fixes: Fixes #323

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 44 lines in your changes missing coverage. Please review.

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Flag	Coverage Δ
unittests	37.16% <0.00%> (+5.14%)	:arrow_up:

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
pkg/auth/xdp_auth_handler.go	0.00% <0.00%> (ø)
pkg/auth/rbac.go	57.42% <0.00%> (+0.66%)	:arrow_up:

... and 6 files with indirect coverage changes

[tacslon]

/hold

[tacslon]

/unhold

[hzxuzhonghu]

Please add some unit tests

[kmesh-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hzxuzhonghu

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Needs approval from an approver in each of these files: - ~~[pkg/auth/OWNERS](https://github.com/kmesh-net/kmesh/blob/main/pkg/auth/OWNERS)~~ [hzxuzhonghu] - ~~[pkg/controller/OWNERS](https://github.com/kmesh-net/kmesh/blob/main/pkg/controller/OWNERS)~~ [hzxuzhonghu] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment