openvpn: add config param verify_client_cert

Option --client-cert-not-required DEPRECATED is deprecated in v2.4 and removed in OpenVPN 2.5.
Replaced by param --verify-client-cert none|optional|require in v2.4 see
https://community.openvpn.net/openvpn/wiki/

 DeprecatedOptions#a--client-cert-not-required

Signed-off-by: Christian Bayer <cave@cavebeat.org>
Signed-off-by: Hans Dedecker <dedeckeh@gmail.com> [PKG_	RELEASE increase]

package/network/services/openvpn/Makefile

@@ -10,7 +10,7 @@ include $(TOPDIR)/rules.mk
 PKG_NAME:=openvpn
 
 PKG_VERSION:=2.4.5
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE_URL:=\
 	https://build.openvpn.net/downloads/releases/ \

package/network/services/openvpn/files/openvpn.options

@@ -132,6 +132,7 @@ txqueuelen
 up
 user
 verb
+verify_client_cert
 verify_x509_name
 x509_username_field
 '