Demonstrations of undump.py, the Linux eBPF/bcc version.

This example trace the kernel function performing receive AP_UNIX socket
packet. Some example output:

Terminal 1, UNIX Socket Server:

```
$ nc -lU /var/tmp/dsocket
# receive from Client
Hello, World
abcdefg
```

Terminal 2, UNIX socket Client:

```
$ nc -U /var/tmp/dsocket
# Input some lines
Hello, World
abcdefg
```

Terminal 3, receive tracing:

```
$ sudo python undump.py -p 49264
Tracing PID=49264 UNIX socket packets ... Hit Ctrl-C to end

# Here print bytes of receive
PID 49264 Recv 13 bytes
   48 65 6c 6c 6f 2c 20 57 6f 72 6c 64 0a
PID 49264 Recv 8 bytes
   61 62 63 64 65 66 67 0a
```

This output shows two packet received by PID 49264(nc -lU /var/tmp/dsocket),
`Hello, World` will be parsed as `48 65 6c 6c 6f 2c 20 57 6f 72 6c 64 0a`, the
`0a` is `Enter`. `abcdefg` will be parsed as `61 62 63 64 65 66 67 0a`.