Combine extra_tun/frame parameter of frame_calculate_payload_overhead

Combine extra_tun/frame parameter of frame_calculate_payload_overhead

Instead of passing a value and a bool just pass the value and 0 if
the caller does not want the value to be added. This also allows
the function to be used by a function without a frame struct.

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Frank Lichtenheld <frank@lichtenheld.com>
Message-Id: <20230210142712.572303-3-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg26223.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>