Adjust Android code after sitnl patch merge

Adjust Android code after sitnl patch merge

It turns out that the only part of Android that still shares routing
code with Linux is the get_default_ipv6 method.

Instead of fixing a method that makes little sense on Android anyway,
have a method that returns a fake ipv6 gateway like for ipv4.

Patch V2: Instead adding ANDROID to a long list of ifdefs, change this
	to a non LINUX ifdef

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20190815121053.18433-2-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg18752.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>