Conditionalize calls to print_default_gateway on !ENABLE_SMALL

Calls to print_default_gateway() depended on #ifdef ENABLE_DEBUG, but
the actual function wasn't compiled in #ifdef ENABLE_SMALL, so the
combination "configure --enable-small --enable-debug" didn't work. Fix.

Fix trac #397

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Message-Id: <1398805779-29376-1-git-send-email-gert@greenie.muc.de>
URL: http://article.gmane.org/gmane.network.openvpn.devel/8670
(cherry picked from commit c29e08a2f33234fb705a8323c0d9e1e07b0773fd)