Inline frame_add_to_extra_tun function and remove frame_defined

Inline frame_add_to_extra_tun function and remove frame_defined

This function has only one usage and is so trivial that an extra
function makes little sense anymore.

frame_defined is no longer used, so remove the function.

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20220621161649.2872985-2-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg24492.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>