socket: remove duplicate expression

Found via cppcheck and compile-tested.

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1416687215-26904-1-git-send-email-yegorslists@googlemail.com>
URL: http://article.gmane.org/gmane.network.openvpn.devel/9263
Signed-off-by: Gert Doering <gert@greenie.muc.de>