sitnl: Clean up type handling

sitnl: Clean up type handling

- Make some type casts explicit. Due to the types used
  in our networking API and the netlink APIs respectively
  this can't be avoided.
- In many cases just use correct types from the start, e.g.
  where we use constants anyway.

Change-Id: I20205ebd06bbf7cbee8c9be93f399961f5b74fcc
Signed-off-by: Frank Lichtenheld <frank@lichtenheld.com>
Acked-by: Antonio Quartulli <antonio@mandelbit.com>
Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1251
Message-Id: <20251007122747.16064-1-gert@greenie.muc.de>
URL: https://sourceforge.net/p/openvpn/mailman/message/59243289/
Signed-off-by: Gert Doering <gert@greenie.muc.de>