tests: Check received prefixes before immediately sending dynamic capabilities (backport #14756)

[mergify]

This is an automatic backport of pull request #14756 done by Mergify.
Cherry-pick of c12b976 has failed:

On branch mergify/bp/dev/9.1/pr-14756
Your branch is up to date with 'origin/dev/9.1'.

You are currently cherry-picking commit c12b976c0.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   tests/topotests/bgp_dynamic_capability/test_bgp_dynamic_capability_graceful_restart.py
	modified:   tests/topotests/bgp_dynamic_capability/test_bgp_dynamic_capability_role.py
	modified:   tests/topotests/bgp_dynamic_capability/test_bgp_dynamic_capability_software_version.py

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   tests/topotests/bgp_dynamic_capability/test_bgp_dynamic_capability_addpath.py
	deleted by us:   tests/topotests/bgp_dynamic_capability/test_bgp_dynamic_capability_orf.py

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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[ton31337]

Manual backport #14763, closing here.