Fix --redirect-private in --dev tap mode.

Fix --redirect-private in --dev tap mode.

When specifying redirect-private option and not specifying route-gateway
or ifconfig options, OpenVPN fails to add the route to the remote host
with the following message:

NOTE: unable to redirect default gateway -- VPN gateway parameter
(--route-gateway or --ifconfig) is missing

In redirect_default_route_to_vpn() the check for remote endpoint happens
even though it is not used by redirect-private - make check conditional
on RG_REROUTE_GW (= --redirect-gateway).

Trac #261

Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20150531120327.GE382@greenie.muc.de>
URL: http://article.gmane.org/gmane.network.openvpn.devel/9761
Signed-off-by: Gert Doering <gert@greenie.muc.de>