Messy code on kernel 5.1.8

Testing with opensnoop.py. The bcc version is v0.10.0

On kernel 5.1.8
```
sudo ./opensnoop.py
PID COMM FD ERR PATH
11721 <...> 9 0 ���
6781 irqbalance 3 0 ���������W�U
6781 irqbalance 3 0 ���������W�U
```

On kernel 3.10.0-957

```
sudo ./opensnoop.py
PID COMM FD ERR PATH
15945 <...> 9 0 /sys/kernel/debug/tracing/trace_pipe
16004 cpio 3 0 /etc/passwd
3445 systemd-journal 29 0 /proc/8823/cgroup
```

Start with opensnoop.py and reproduce the reported output on kernel 5.1.8 and 3.10.0-957 using the commands in the issue. Compare the displayed PATH values with the expected readable paths; done means opensnoop.py no longer emits garbled output for the affected kernel.

Written by the indexing model from the issue text.