Fix compilation on Windows

Fix compilation on Windows

The local member in struct link_socket_address went away a while ago.
Fixing the code to compile again under Windows. While there, also
fix the code to deal with struct link_socket_info.af == AF_UNSPEC

(The breakage this fixes was introduced by the dual-stack socket
rework, most likely commit 6c5db192c30ff0c6b89e2e0aefec00329de39302)

Signed-off-by: Heiko Hund <heiko.hund@sophos.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1416068708-6871-1-git-send-email-heiko.hund@sophos.com>
URL: http://article.gmane.org/gmane.network.openvpn.devel/9228
Signed-off-by: Gert Doering <gert@greenie.muc.de>