package/ulogd: add optional support for jansson

When jansson was compiled before, ulogd will use it as optional
dependency:

$ output/host/usr/bin/i586-buildroot-linux-uclibc-readelf -a output/target/usr/lib/ulogd/ulogd_output_JSON.so | grep NEEDED
 0x00000001 (NEEDED)                     Shared library: [libjansson.so.4]
 0x00000001 (NEEDED)                     Shared library: [libc.so.1]

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/ulogd/ulogd.mk

@@ -29,4 +29,11 @@ else
 ULOGD_CONF_OPTS += --with-mysql=no --without-sqlite
 endif
 
+ifeq ($(BR2_PACKAGE_JANSSON),y)
+ULOGD_CONF_OPTS += --with-jansson
+ULOGD_DEPENDENCIES += jansson
+else
+ULOGD_CONF_OPTS += --without-jansson
+endif
+
 $(eval $(autotools-package))