tun: extract close_tun_handle into its own fucntion and print correct type

tun: extract close_tun_handle into its own fucntion and print correct type

This moves closing the tun handle into its own function and also prints
the adapter type we are operating on, instead hardcoding it to
tap-windows.

While at it, set the handle to NULL after closing, to prevent a double
close due to multiple invocations of this helper.

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Signed-off-by: Antonio Quartulli <a@unstable.cc>
Acked-by: Frank Lichtenheld <frank@lichtenheld.com>
Message-Id: <20220624083809.23487-18-a@unstable.cc>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg24527.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>