package/openvpn: bump version to 2.6.4

Changelog:
https://github.com/OpenVPN/openvpn/blob/release/2.6/ChangeLog
https://github.com/OpenVPN/openvpn/blob/release/2.6/Changes.rst

Added mandatory dependency to libcap-ng due to upstream commit
https://github.com/OpenVPN/openvpn/commit/2e359a088226ab1e5ee41fbab27d38d8a8d192ac

Added optional dependency to libnl due to upstream commit
https://github.com/OpenVPN/openvpn/commit/f63c9b1edbda41491ba2e05ff706bf0233903cb6

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/openvpn/Config.in

@@ -1,6 +1,7 @@
 config BR2_PACKAGE_OPENVPN
 	bool "openvpn"
 	depends on BR2_USE_MMU # fork()
+	select BR2_PACKAGE_LIBCAP_NG
 	select BR2_PACKAGE_OPENSSL if !BR2_PACKAGE_MBEDTLS
 	select BR2_PACKAGE_LIBOPENSSL_ENABLE_DES if BR2_PACKAGE_LIBOPENSSL
 	help

package/openvpn/openvpn.hash

@@ -1,3 +1,3 @@
 # Locally calculated after checking signature
-sha256  08340a389905c84196b6cd750add1bc0fa2d46a1afebfd589c24120946c13e68  openvpn-2.5.7.tar.gz
+sha256  371a2a323a99a79299b9b4caa4a31bc7b2cdff63236e68d429f3ee50e75f3dd4  openvpn-2.6.4.tar.gz
 sha256  1fcb78d7e478bb8a9408010bdc91b36e213b1facfad093df3f7ce7e28af19043  COPYRIGHT.GPL

package/openvpn/openvpn.mk

@@ -4,9 +4,9 @@
 #
 ################################################################################
 
-OPENVPN_VERSION = 2.5.7
+OPENVPN_VERSION = 2.6.4
 OPENVPN_SITE = https://swupdate.openvpn.net/community/releases
-OPENVPN_DEPENDENCIES = host-pkgconf
+OPENVPN_DEPENDENCIES = host-pkgconf libcap-ng
 OPENVPN_LICENSE = GPL-2.0
 OPENVPN_LICENSE_FILES = COPYRIGHT.GPL
 OPENVPN_CPE_ID_VENDOR = openvpn
@@ -16,6 +16,13 @@ OPENVPN_CONF_OPTS = \
 	$(if $(BR2_STATIC_LIBS),--disable-plugins)
 OPENVPN_CONF_ENV = NETSTAT=/bin/netstat
 
+ifeq ($(BR2_PACKAGE_LIBNL),y)
+OPENVPN_CONF_OPTS += --enable-dco
+OPENVPN_DEPENDENCIES += libnl
+else
+OPENVPN_CONF_OPTS += --disable-dco
+endif
+
 ifeq ($(BR2_PACKAGE_OPENVPN_SMALL),y)
 OPENVPN_CONF_OPTS += \
 	--enable-small \