To reproduce:

* Install fresh Fedora 34 VM
* Compile Bitcoin Core and run `./test/functional/p2p_dns_seeds.py`
{
        allowed_syscalls.insert(__NR_clock_nanosleep); 
        allowed_syscalls.insert(__NR_nanosleep);       
    }
    void AllowUmask()
    {
        allowed_syscalls.insert(__NR_umask); 
    }
    
    
    
    
    std::vector<sock_filter> BuildFilter(SyscallSandboxAction default_action)
    {
        std::vector<sock_filter> bpf_policy;
        
        bpf_policy.push_back(BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct seccomp_data, arch)));
        
        bpf_policy.push_back(BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, AUDIT_ARCH_X86_64, 1, 0));
        bpf_policy.push_back(BPF_STMT(BPF_RET + BPF_K, SECCOMP_RET_KILL_PROCESS));
        
        bpf_policy.push_back(BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct seccomp_data, nr)));
        for (const uint32_t allowed_syscall : allowed_syscalls) {
            
            bpf_policy.push_back(BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, allowed_syscall, 0, 1));
            bpf_policy.push_back(BPF_STMT(BPF_RET + BPF_K, SECCOMP_RET_ALLOW));
        }
        switch (default_action) {
        case SyscallSandboxAction::KILL_PROCESS: