bird2: replace gcc flag workaround with patch fixing alignment issues

Previously, we used the -mno-unaligned-access flag to instruct GCC to
forbid unaligned memory access on arm processors. This was a workaround
for alignment issues that caused crashes.

This commit imports a patch from the BIRD mailing list discussion [0]
that resolves the alignment issue by modifying the net_addr structure,
removing the need for the GCC flag. The patch addresses the alignment
problem more efficiently and avoids the performance, code size, and
hardware optimization drawbacks of the flag.

[0] - http://trubka.network.cz/pipermail/bird-users/2024-December/017957.html

Signed-off-by: Nick Hainke <[email protected]>

bird2/Makefile

@@ -97,10 +97,6 @@ protocols, telling BIRD to show various information, telling it to show
 a routing table filtered by a filter, or asking BIRD to reconfigure.
 endef
 
-ifeq ($(ARCH),arm)
-TARGET_CFLAGS+=-mno-unaligned-access
-endif
-
 CONFIGURE_ARGS += --disable-libssh
 
 define Package/bird2/conffiles

bird2/patches/001-fix-net_addr-alignment-for-armv7.patch

@@ -0,0 +1,44 @@
+From b4e8108cb2995f45d63105f6b179d8e4a155eab5 Mon Sep 17 00:00:00 2001
+From: Nick Hainke <[email protected]>
+Date: Tue, 17 Dec 2024 23:38:45 +0100
+Subject: [PATCH] Fix net_addr alignment for armv7
+
+The patch originates from the mailing list discussion [0].
+
+On armv7 platforms, the `net_addr` structure caused alignment issues due
+to the use of `u64 align[0]`, which requires 8-byte alignment. This led
+to crashes on systems with stricter alignment rules.
+
+This patch changes the alignment to `u32 align[0]`, which resolves the
+crashes. However, this change may still cause issues with VPN network types
+that rely on stricter alignment.
+
+Previously, we used a workaround with `-mno-unaligned-access` [1,2],
+which prevents unaligned memory crashes but comes at the cost of reduced
+performance, larger code size, and missed hardware optimizations. Applying
+this patch is a better solution, even if VPN network types may still face
+problems. Alignment issues are expected to be properly resolved in the
+upcoming BIRD 3 release, so this patch will not be merged into upstream BIRD
+since it also originates from the BIRD mailing list discussion.
+
+[0] - http://trubka.network.cz/pipermail/bird-users/2024-December/017957.html
+[1] - https://github.com/freifunk-berlin/falter-packages/commit/fcce390fc57b44593fe969f1063c6ba711fc7f9b
+[2] - https://github.com/openwrt/routing/commit/0209a1f3be5d0d227c34c7e73ff779ef7dcc533e
+
+Signed-off-by: Nick Hainke <[email protected]>
+---
+---
+ lib/net.h | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+--- a/lib/net.h
++++ b/lib/net.h
+@@ -51,7 +51,7 @@ typedef struct net_addr {
+   u8 pxlen;
+   u16 length;
+   u8 data[20];
+-  u64 align[0];
++  u32 align[0];
+ } net_addr;
+
+ typedef struct net_addr_ip4 {