util/linuxfw: add new arch build constraints

Exclide GOARCHs including: mips, mips64, mips64le, mipsle, riscv64.
These archs are not supported by gvisor.dev/gvisor/pkg/hostarch.

Fixes: #391
Signed-off-by: KevinLiang10 <kevinliang@tailscale.com>

util/linuxfw/linuxfw_struct_linux_test.go

@@ -1,7 +1,8 @@
 // Copyright (c) Tailscale Inc & AUTHORS
 // SPDX-License-Identifier: BSD-3-Clause
 
-//go:build linux && !(386 || loong64 || arm || armbe)
+// TODO(#8502): add support for more architectures
+//go:build linux && (arm64 || amd64)
 
 package linuxfw