Remove support for Linux 2.2 configuration fallback

Remove support for Linux 2.2 configuration fallback

When configuring OpenVPN nowadays, the TUN/TAP configuration can
sometimes jump into the Linux 2.2 fallback code paths, which will
also fails.  The reason it jumps into fallback mode is that the
tun/tap device already exists or that /dev/net/tun does not exist.
This can be very confusing, as /dev/tunX which the fallback mode tries
to use, does not exist on Linux 2.4 and newer.

Considering that the last Linux 2.2 update was released 25-Feb-2004
and the first Linux 2.4 release came 04-Jan-2001, there are no
reasonable reasons to help users to stay on outdated kernels.
I consider this extra code path just waste of bytes ... so lets make
the world simpler.

Signed-off-by: David Sommerseth <davids@redhat.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit ce637abdafdc19547fc97192033a4d1703ecaf23)