Change hash iv to a be a fixed sized array

Change hash iv to a be a fixed sized array

While for our own hash function, always using an uint32_t works well, it does
not work very well if we move to another hash function like siphash that
requires a larger key.

To avoid allocating a specific context, change the API to be a fixed size
array of size 4. This define allows use to easily change it to a larger
value if we use hash functions that require larger keys.

Change-Id: If47c7d920b2fa4047b7db03fcde821899839324d
Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Frank Lichtenheld <frank@lichtenheld.com>
Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1571
Message-Id: <20260806102926.28206-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg38162.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>