libdnet: always build a static library

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

diff --git a/libdnet-stripped/configure.gnu b/libdnet-stripped/configure.gnu
--- /dev/null
+++ b/libdnet-stripped/configure.gnu
@@ -0,0 +1,3 @@
+#!/bin/sh
+
+exec "${0%.gnu}" "${@}" --enable-static --disable-shared
