add 3rd party/custom patches

3rd patchs (in alphabetical order):
- bbr3
- ntsync5
- openwrt
- pf-kernel
- xanmod
- zen

no configuration changes for now

debian/patches/patchset-zen/sauce/0004-ZEN-Disable-stack-conservation-for-GCC.patch

@@ -0,0 +1,29 @@
+From 89a4975b413afa5f591c7a18109d35b5e848b582 Mon Sep 17 00:00:00 2001
+From: Sultan Alsawaf <sultan@kerneltoast.com>
+Date: Sun, 8 Mar 2020 00:31:35 -0800
+Subject: ZEN: Disable stack conservation for GCC
+
+There's plenty of room on the stack for a few more inlined bytes here
+and there. The measured stack usage at runtime is still safe without
+this, and performance is surely improved at a microscopic level, so
+remove it.
+
+Signed-off-by: Sultan Alsawaf <sultan@kerneltoast.com>
+---
+ Makefile | 5 -----
+ 1 file changed, 5 deletions(-)
+
+--- a/Makefile
++++ b/Makefile
+@@ -1003,11 +1003,6 @@ KBUILD_CFLAGS	+= -fno-strict-overflow
+ # Make sure -fstack-check isn't enabled (like gentoo apparently did)
+ KBUILD_CFLAGS  += -fno-stack-check
+ 
+-# conserve stack if available
+-ifdef CONFIG_CC_IS_GCC
+-KBUILD_CFLAGS   += -fconserve-stack
+-endif
+-
+ # change __FILE__ to the relative path from the srctree
+ KBUILD_CPPFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
+