[roll] Roll fuchsia [netstack3] Update TCP CUBIC to RFC 9438

The TCP CUBIC Specification has been updated from RFC 8312 to RFC 9438.
In practice, most of the algorithm is unchanged, however there are a few
key differences:
* When updating the cwnd with the cubic_window function, the target is
  clamped to between 1 and 1.5 cwnds. This adds an upperbound to the
  growth rate.
* The TCP-Friendly Region defined in RFC 8312 was renamed to the
  Reno-Friendly Region. It aspires to compute a cwnd equivalent to Reno
  Congestion Control.
* The equation used to calculate w_est in the Reno-Friendly region
  changed in two ways: 1) It is now based on ACKed segments rather than
  elapsed time, and 2) the ALPHA_CUBIC parameter is set to 1.0 when
  w_est >= cwnd_prior. When this is true, cwnd growth is more aggressive
  in the Reno-friendly region than it would have been in the
  TCP-Friendly Region from RFC 8312. This brings the algorithm closer
  inline with true Reno Congestion Control.
* When reducing `cwnd` and `ssthresh` in response to a congestion event,
  the multiplicative decrease is based on `flight_size` based on `cwnd`.
  The `flight_size` is the amount of data sent but not yet acknowledged,
  which is semantically equivalent to the `pipe` tracked by SACK.

The rest of the diff in the CL is cosmetic changes: Updating RFC
citations & reflowing code.

Original-Original-Fixed: 404908966
Original-Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1614548
Original-Original-Revision: 8457d80713d4be559c8d7088dffda830f750c10f
GitOrigin-RevId: beef7f56cc9c66a77de5e011c51fe88bc7b7366c
Change-Id: Ifb6e29ab93f632f547e301e0b0ab788df194967a
Reviewed-on: https://fuchsia-review.googlesource.com/c/integration/+/1678869
Cr-Commit-Position: refs/heads/main@{#195535}