siphash24() is wildly used by projects nowadays.

It's certainly slower then our djb hashing that we used before.
But quite likely it's fast enough for us, given how wildly it is
used. I think it would be hard to profile NetworkManager to show
that the performance of hash tables is the issue, be it with
djb or siphash24.

Certainly with siphash24() it's much harder to exploit the hashing
algorithm to cause worst case hash operations (provided that the
seed is kept private). Does this better resistance against a denial
of service matter for us? Probably not, but let's better be safe then
sorry.

Note that systemd's implementation uses a different seed for each hash
table (at least, after the hash table grows to a certain size).
We don't do that and use only one global seed.