Now with basic support for the Array Networks SSL VPN protocol.

Also fix the OpenSSL build. OpenConnect requires support for deprecated APIs,
for the time being, so select them if compiling against OpenSSL.

Signed-off-by: Rui Salvaterra <rsalvaterra@gmail.com>
(cherry picked from commit a85a057b14)

Add a new build configuration option for openconnect and let it link
against libstoken if instructed to. Two new uci configuration variables
are introduced: "token_mode" and "token_secret" to allow openconnect to
use those.

Signed-off-by: Florian Fainelli <florian@openwrt.org>