Fix socks_proxy_port pointing to invalid data

Fix socks_proxy_port pointing to invalid data

When setting the SOCKS proxy through the management interface, the
socks_proxy_port pointer would be set to a value that's no longer valid
by the time it's used by do_preresolve_host.

Signed-off-by: Thomas Veerman <thomas.veerman@wanwire.net>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <20170707195941.61773-1-thomas.veerman@wanwire.net>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg15018.html
Signed-off-by: David Sommerseth <davids@openvpn.net>
(cherry picked from commit aa9d3a5bdc5a1b395d37fbb8abb3ed6166856a1a)