Fix include for system lz4.

make-linux.mk

@@ -41,6 +41,7 @@ ifeq ($(wildcard /usr/include/lz4.h),)
 	OBJS+=ext/lz4/lz4.o
 else
 	LDLIBS+=-llz4
+	DEFS+=-DZT_USE_SYSTEM_LZ4
 endif
 ifeq ($(wildcard /usr/include/http_parser.h),)
 	OBJS+=ext/http-parser/http_parser.o

node/Packet.hpp

@@ -34,7 +34,11 @@
 #include "Utils.hpp"
 #include "Buffer.hpp"
 
+#ifdef ZT_USE_SYSTEM_LZ4
+#include <lz4.h>
+#else
 #include "../ext/lz4/lz4.h"
+#endif
 
 /**
  * Protocol version -- incremented only for major changes