openvswitch: use https download url

At the time of this writing, Open vSwitch official website suggests
http://openvswitch.org whose https couterpart uses a self-signed
certificate, but it redirects to http://www.openvswitch.org, which has a
working https equivalent.

Reported-by: Rosen Penev <rosenp@gmail.com>
Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>

net/openvswitch/Makefile

@@ -19,7 +19,7 @@ PKG_LICENSE_FILES:=COPYING
 PKG_USE_MIPS16:=0
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
-PKG_SOURCE_URL:=http://openvswitch.org/releases/
+PKG_SOURCE_URL:=https://www.openvswitch.org/releases/
 PKG_HASH:=8d1c439e26d7044f0ec823c7fef1b00b7c6465da0b83a7d0cf3191ed1dc43893
 
 PKG_BUILD_DEPENDS:=python/host