In PR tailscale/corp#30448, we originally decided to break ties using
SHA256 for our rendezvous hashing algorithm. Now that we’ve had some
experience with it, we think that FNV-1a is a better choice. It
distributes bits evenly, it’s much faster, and it doesn’t need to be
cryptographically secure. The FNV designers recommend FNV-1a over the
deprecated FNV-1.
This PR makes the switch and updates the related tests, since changing
the algorithm changes which stable pick gets selected. As of 2026-05,
this is the best time to make this change, since there are almost no
clients in the wild with traffic steering enabled.
Updates #17366
Updates tailscale/corp#29964
Updates tailscale/corp#29966
Updates tailscale/corp#33033
Signed-off-by: Simon Law <sfllaw@tailscale.com>
7dabebc691