ptpd2: fix static linking

Do the same as in commit b64a06d7b70bd7b160826bf9b97e60e18171913d
to avoid missing libraries needed by libpcap. Fixes:
http://autobuild.buildroot.net/results/1a1/1a1dadfa2b22074d401b013606f0cede66efe826/

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/ptpd2/ptpd2.mk

@@ -13,6 +13,10 @@ PTPD2_AUTORECONF = YES
 PTPD2_LICENSE = BSD-2c
 PTPD2_LICENSE_FILES = COPYRIGHT
 
+ifeq ($(BR2_PREFER_STATIC_LIB),y)
+	PTPD2_CONF_OPT += LIBS="$(shell $(STAGING_DIR)/usr/bin/pcap-config --static --additional-libs)"
+endif
+
 ifeq ($(BR2_PACKAGE_NETSNMP),y)
 	PTPD2_CONF_ENV += ac_cv_path_PATH_NET_SNMP_CONFIG=$(STAGING_DIR)/usr/bin/net-snmp-config
 	PTPD2_DEPENDENCIES += netsnmp