Defer active path activation

[Guillaume Hetier (guhetier)]

Description

Defers active-path changes until receive processing no longer holds pointers into the path array.

Receiving a valid packet containing non-probing frames on a path makes this path active.
However, setting a path as active moves it to the front of the path array, which can potentially invalidate pointers to paths.

To avoid this:

• track which path needs to be active
• only make it active once all packets in the receive operation are processed

The active path is mostly needed to send (it is by definition the path the connection uses to send packets), so it isn't a problem to defer the operation until the end of the receive loop. A side benefit is that it avoids multiple updates in sequence if multiple migrations would be triggered in a single receive operation.

Testing

CI and local testing

Documentation

No documentation impact.

[Guillaume Hetier (guhetier)]

Note to reviewer: Known gap, addressed in the next PR in the PR stack when this QuicPathRemove is also deferred to after processing the received packets.

[codecov]

Codecov Report

❌ Patch coverage is 93.93939% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.57%. Comparing base (7e5c632) to head (64e50bd).

Files with missing lines	Patch %	Lines
src/core/connection.c	92.30%	1 Missing ⚠️
src/core/path.c	95.00%	1 Missing ⚠️

Additional details and impacted files

@@                          Coverage Diff                          @@
##           guhetier/reafactor_network_path_2    #6273      +/-   ##
=====================================================================
+ Coverage                              85.34%   85.57%   +0.22%     
=====================================================================
  Files                                     60       60              
  Lines                                  19008    19033      +25     
=====================================================================
+ Hits                                   16222    16287      +65     
+ Misses                                  2786     2746      -40     

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