perl-net-ping: add missing license declaration

Signed-off-by: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/perl-net-ping/perl-net-ping.mk

@@ -7,6 +7,7 @@
 PERL_NET_PING_VERSION = 2.68
 PERL_NET_PING_SOURCE = Net-Ping-$(PERL_NET_PING_VERSION).tar.gz
 PERL_NET_PING_SITE = $(BR2_CPAN_MIRROR)/authors/id/R/RU/RURBAN
+PERL_NET_PING_LICENSE = Artistic or GPL-1.0+
 PERL_NET_PING_LICENSE_FILES = README
 
 $(eval $(perl-package))