To reproduce:

* Install fresh Fedora 34 VM
* Compile Bitcoin Core and run `./test/functional/p2p_dns_seeds.py`
#if defined(USE_SYSCALL_SANDBOX)
    if (!g_syscall_sandbox_enabled) {
        return;
    }
    SeccompPolicyBuilder seccomp_policy_builder;
    switch (syscall_policy) {
    case SyscallSandboxPolicy::INITIALIZATION: 
        
        
        
        
        
        
        
        seccomp_policy_builder.AllowFileSystem();
        seccomp_policy_builder.AllowNetwork();
        break;
    case SyscallSandboxPolicy::INITIALIZATION_DNS_SEED: 
        seccomp_policy_builder.AllowFileSystem();
        seccomp_policy_builder.AllowNetwork();
        break;
    case SyscallSandboxPolicy::INITIALIZATION_LOAD_BLOCKS: 
        seccomp_policy_builder.AllowFileSystem();
        break;
    case SyscallSandboxPolicy::INITIALIZATION_MAP_PORT: 
        seccomp_policy_builder.AllowFileSystem();
        seccomp_policy_builder.AllowNetwork();
        break;
    case SyscallSandboxPolicy::MESSAGE_HANDLER: 
        seccomp_policy_builder.AllowFileSystem();