pkg: improve get forwarded host

[rleungx]

What problem does this PR solve?

Issue Number: ref #7897.

What is changed and how does it work?

$ benchstat old.txt new.txt
goos: linux
goarch: amd64
pkg: github.com/tikv/pd/pkg/utils/grpcutil
cpu: Intel(R) Xeon(R) Gold 6240 CPU @ 2.60GHz
                               │   old.txt    │               new.txt               │
                               │    sec/op    │   sec/op     vs base                │
GetForwardedHostWithNoValue-72   350.15n ± 5%   59.15n ± 1%  -83.11% (p=0.000 n=10)

                               │  old.txt   │              new.txt              │
                               │    B/op    │   B/op    vs base                 │
GetForwardedHostWithNoValue-72   416.0 ± 0%   0.0 ± 0%  -100.00% (p=0.000 n=10)

                               │  old.txt   │               new.txt               │
                               │ allocs/op  │ allocs/op   vs base                 │
GetForwardedHostWithNoValue-72   3.000 ± 0%   0.000 ± 0%  -100.00% (p=0.000 n=10)

Check List

Tests

• Unit test

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• lhy1024
• nolouch

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

The full list of commands accepted by this bot can be found here.

Reviewer can indicate their review by submitting an approval review.
Reviewer can cancel approval by submitting a request changes review.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.45%. Comparing base (e105836) to head (017c347).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8182      +/-   ##
==========================================
+ Coverage   77.39%   77.45%   +0.06%     
==========================================
  Files         471      471              
  Lines       61367    61364       -3     
==========================================
+ Hits        47492    47528      +36     
+ Misses      10311    10275      -36     
+ Partials     3564     3561       -3     

Flag	Coverage Δ
unittests	77.45% <100.00%> (+0.06%)	⬆️

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

[nolouch]

/merge

[ti-chi-bot]

@nolouch: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

You only need to trigger /merge once, and if the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

If you have any questions about the PR merge process, please refer to pr process.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 017c347