Workaround broken Android 4.4 VpnService API for persist-tun mode

Workaround broken Android 4.4 VpnService API for persist-tun mode

In Android 4.4 it is not possible to open a new tun device and then close
the old tun device without breaking the whole VPNService stack until the
device is rebooted.

Add new management method to ask the UI what method should be taken to
ensure the optimal solution for the situation.  Then do open-before-close
or close-before-open inside open_tun() as requested.

Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1395407925-25518-4-git-send-email-arne@rfc2549.org>
URL: http://article.gmane.org/gmane.network.openvpn.devel/8373

Signed-off-by: Gert Doering <gert@greenie.muc.de>