package/libmodbus: add LIBMODBUS_CPE_ID_VENDOR

cpe:2.3:a:libmodbus:libmodbus is a valid CPE identifier for this
package:

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

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
(cherry picked from commit 8910dc505a77952fafeee326ca04da5345cdea96)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/libmodbus/libmodbus.mk

@@ -8,6 +8,7 @@ LIBMODBUS_VERSION = 3.1.6
 LIBMODBUS_SITE = http://libmodbus.org/releases
 LIBMODBUS_LICENSE = LGPL-2.1+
 LIBMODBUS_LICENSE_FILES = COPYING.LESSER
+LIBMODBUS_CPE_ID_VENDOR = libmodbus
 LIBMODBUS_INSTALL_STAGING = YES
 LIBMODBUS_CONF_OPTS = --without-documentation --disable-tests