ssl_pkt: Avoid conversion warnings

ssl_pkt: Avoid conversion warnings

I considered changing opcode to be uint8_t directly, but
most code treats it as int now, so that would be a much
bigger change. Similar for key_id.

Change-Id: I2a1786b2bf15852222c28e1b73ab7edbb5f19d7f
Signed-off-by: Frank Lichtenheld <frank@lichtenheld.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1360
Message-Id: <20251117074921.26531-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg34501.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>