package/libdnet: don't override dependencies

Don't override LIBDNET_DEPENDENCIES in a conditional

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
(cherry picked from commit ea21670ee830bfd86dca47434ef01c61da2a36cd)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/libdnet/libdnet.mk

@@ -16,7 +16,7 @@ LIBDNET_CONF_OPTS = \
 LIBDNET_CONFIG_SCRIPTS = dnet-config
 
 ifneq ($(BR2_PACKAGE_LIBDNET_PYTHON),)
-LIBDNET_DEPENDENCIES = python
+LIBDNET_DEPENDENCIES += python
 LIBDNET_CONF_OPTS += --with-python
 LIBDNET_MAKE_OPTS = PYINCDIR=$(STAGING_DIR)/usr/include/python$(PYTHON_VERSION_MAJOR) PYLIBDIR=$(STAGING_DIR)/usr/lib
 LIBDNET_INSTALL_TARGET_OPTS = $(LIBDNET_MAKE_OPTS) DESTDIR=$(TARGET_DIR) INSTALL_STRIP_FLAG=-s install-exec