package/libevent: set LIBEVENT_CPE_ID_VALID

cpe:2.3:a:libevent_project:libevent is a valid CPE identifier for this
package:

  https://nvd.nist.gov/products/cpe/search/results?namingFormat=2.3&keyword=cpe%3A2.3%3Aa%3Alibevent_project%3Alibevent

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/libevent/libevent.mk

@@ -10,6 +10,7 @@ LIBEVENT_SOURCE = libevent-$(LIBEVENT_VERSION)-stable.tar.gz
 LIBEVENT_INSTALL_STAGING = YES
 LIBEVENT_LICENSE = BSD-3-Clause, OpenBSD
 LIBEVENT_LICENSE_FILES = LICENSE
+LIBEVENT_CPE_ID_VALID = YES
 LIBEVENT_CONF_OPTS = \
 	--disable-libevent-regress \
 	--disable-samples