wireguard: allowedips: avoid unaligned 64-bit memory accesses

On the parisc platform, the kernel issues kernel warnings because
swap_endian() tries to load a 128-bit IPv6 address from an unaligned
memory location:

 Kernel: unaligned access to 0x55f4688c in wg_allowedips_insert_v6+0x2c/0x80 [wireguard] (iir 0xf3010df)
 Kernel: unaligned access to 0x55f46884 in wg_allowedips_insert_v6+0x38/0x80 [wireguard] (iir 0xf2010dc)

Avoid such unaligned memory accesses by instead using the
get_unaligned_be64() helper macro.
Signed-off-by: Helge Deller <deller@gmx.de>
[Jason: replace src[8] in original patch with src+8]
Cc: stable@vger.kernel.org
Fixes: e7096c13 ("net: WireGuard secure network tunnel")
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Link: https://patch.msgid.link/20240704154517.1572127-3-Jason@zx2c4.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/wireguard/allowedips.c

@@ -15,8 +15,8 @@ static void swap_endian(u8 *dst, const u8 *src, u8 bits)
 	if (bits == 32) {
 		*(u32 *)dst = be32_to_cpu(*(const __be32 *)src);
 	} else if (bits == 128) {
-		((u64 *)dst)[0] = be64_to_cpu(((const __be64 *)src)[0]);
-		((u64 *)dst)[1] = be64_to_cpu(((const __be64 *)src)[1]);
+		((u64 *)dst)[0] = get_unaligned_be64(src);
+		((u64 *)dst)[1] = get_unaligned_be64(src + 8);
 	}
 }