Respect IncludeLoopback in UDPMuxDefault

[dinvlad]

Description

Currently, when using UDPMuxDefault with unspecified address, the loopback address is included by default, but agentConfig.IncludeLoopback is not respected when gathering local candidates.

The same holds true when UDPMuxDefault is configured with a loopback address, but agentConfig.IncludeLoopback is not explicitly set to true.

This commit adds an extra check to gatherCandidatesLocalUDPMux() for respecting that setting in both cases.

Reference issue

[codecov[bot]]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Files	Coverage Δ
gather.go	0.00% <0.00%> (-66.79%)	:arrow_down:

... and 30 files with indirect coverage changes

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 78.53%. Comparing base (cb8a47a) to head (5427ec0).

:exclamation: Current head 5427ec0 differs from pull request most recent head b44ef41. Consider uploading reports for the commit b44ef41 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #625      +/-   ##
==========================================
- Coverage   78.78%   78.53%   -0.26%     
==========================================
  Files          42       42              
  Lines        4431     4398      -33     
==========================================
- Hits         3491     3454      -37     
- Misses        723      729       +6     
+ Partials      217      215       -2     

Flag	Coverage Δ
go	78.53% <100.00%> (-0.26%)	:arrow_down:
wasm	22.34% <0.00%> (-0.90%)	:arrow_down:

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[Sean-Der]

Cherry-picked with 77cc354d7ff64da809e1b2b36b27ff443f7415ef