zerotier: update to version 1.2.8

Signed-off-by: Moritz Warning <moritzwarning@web.de>

net/zerotier/patches/0004-accept-external-linker-flags.patch

@@ -0,0 +1,25 @@
+From a2cf8bf645d25f18cbc2ed7ad4b9a25725811afd Mon Sep 17 00:00:00 2001
+From: Moritz Warning <moritzwarning@web.de>
+Date: Wed, 2 May 2018 16:06:46 +0200
+Subject: [PATCH 4/4] accept external linker flags
+
+---
+ make-linux.mk | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/make-linux.mk b/make-linux.mk
+index 49e14f70..8e766bfb 100644
+--- a/make-linux.mk
++++ b/make-linux.mk
+@@ -75,7 +75,7 @@ else
+ 	override CFLAGS+=-Wall -Wno-deprecated -pthread $(INCLUDES) -DNDEBUG $(DEFS)
+ 	CXXFLAGS?=-O3 -fstack-protector
+ 	override CXXFLAGS+=-Wall -Wno-deprecated -std=c++11 -pthread $(INCLUDES) -DNDEBUG $(DEFS)
+-	LDFLAGS=-Wl,-z,relro,-z,now
++	LDFLAGS+=-Wl,-z,relro,-z,now
+ 	STRIP?=strip
+ 	STRIP+=--strip-all
+ endif
+-- 
+2.17.0
+