[15896] Fix selection of output locators (backport #3003)

[mergify]

This is an automatic backport of pull request #3003 done by Mergify.
Cherry-pick of 23a788d has failed:

On branch mergify/bp/2.7.x/pr-3003
Your branch is up to date with 'origin/2.7.x'.

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  (fix conflicts and run "git cherry-pick --continue")
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Changes to be committed:
	modified:   include/fastdds/rtps/transport/test_UDPv4TransportDescriptor.h
	modified:   include/fastdds/rtps/writer/StatefulWriter.h
	modified:   src/cpp/rtps/messages/RTPSMessageGroup.cpp
	modified:   src/cpp/rtps/transport/test_UDPv4Transport.cpp
	modified:   src/cpp/rtps/transport/test_UDPv4Transport.h
	modified:   src/cpp/rtps/writer/StatefulWriter.cpp
	modified:   test/blackbox/common/BlackboxTestsDiscovery.cpp

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   src/cpp/rtps/writer/StatelessWriter.cpp
	both modified:   test/blackbox/api/dds-pim/PubSubReader.hpp
	both modified:   test/blackbox/api/dds-pim/PubSubWriter.hpp
	both modified:   test/blackbox/api/fastrtps_deprecated/PubSubReader.hpp
	both modified:   test/blackbox/api/fastrtps_deprecated/PubSubWriter.hpp

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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[MiguelCompany]

@richiprosima Please test this