syncthing: add a patch to increase UDP buffer size

syncthing uses quic-go which warns about insufficient buffer size, so let's increase it:
failed to sufficiently increase receive buffer size (was: 176 kiB, wanted: 2048 kiB, got: 352 kiB). See https://github.com/lucas-clemente/quic-go/wiki/UDP-Receive-Buffer-Size for details.

patches/packages/branding/0003-syncthing-add-a-patch-to-increase-UDP-buffer-size.patch

+From 7cb12d5574ef429b3ca267c5bc3658280859fd92 Mon Sep 17 00:00:00 2001
+From: Michal Vasilek <michal.vasilek@nic.cz>
+Date: Thu, 5 May 2022 15:13:43 +0200
+Subject: [PATCH] syncthing: add a patch to increase UDP buffer size
+
+syncthing uses quic-go which warns about insufficient buffer size, so let's increase it:
+failed to sufficiently increase receive buffer size (was: 176 kiB, wanted: 2048 kiB, got: 352 kiB). See https://github.com/lucas-clemente/quic-go/wiki/UDP-Receive-Buffer-Size for details.
+Also reference: https://github.com/openwrt/packages/pull/18452
+
+Signed-off-by: Michal Vasilek <michal.vasilek@nic.cz>
+---
+ .../syncthing/files/etc/sysctl.d/90-syncthing-udp-buffer.conf  | 3 +++
+ 1 file changed, 3 insertions(+)
+ create mode 100644 utils/syncthing/files/etc/sysctl.d/90-syncthing-udp-buffer.conf
+
+diff --git a/utils/syncthing/files/etc/sysctl.d/90-syncthing-udp-buffer.conf b/utils/syncthing/files/etc/sysctl.d/90-syncthing-udp-buffer.conf
+new file mode 100644
+index 000000000..334dabb4d
+--- /dev/null
++++ b/utils/syncthing/files/etc/sysctl.d/90-syncthing-udp-buffer.conf
+@@ -0,0 +1,3 @@
++# syncthing uses quic-go which warns about insufficient buffer size, so let's increase it
++# failed to sufficiently increase receive buffer size (was: 176 kiB, wanted: 2048 kiB, got: 352 kiB). See https://github.com/lucas-clemente/quic-go/wiki/UDP-Receive-Buffer-Size for details.
++net.core.rmem_max=2500000
+-- 
+2.36.0
+