Switch back to TAP-Windows as default driver on Windows
This mostly reverts commit 8c1d2de0.
It appears that Wintun is not fully stable yet for OpenConnect VPN connections. See #338 (closed) for two reports of instability (with #324 (closed) as a possible third), including one where switching to TAP-Windows clearly resolved the issue.
Per #338 (comment 731175712), we should revert to installing and using TAP-Windows by default until we can figure out why.
OpenConnect will continue to install Wintun, and to use it if and only if TAP-Windows is unavailable, but will issue a loud warning about potential instability to the log.
Edited by Daniel Lenski