ng_tag does can operator on arbitary data of mbuf_tags.
This only works for any data sets.
```
ngctl
+ mkpeer . tag t t
+ msg t sethookin { thisHook="t" tag_len=4 tag_data=[1] }
```
works. But the following does not:
```
+ msg t sethookin { thisHook="t" tag_len=1 tag_data=[1] }
ngctl: send msg: Invalid argument
```
Especially in the case of checking for mbuf_tag values, the length
of checked data is important.
The reason behind this behavoir is, that the record size
is padded to the next multiple of the alignment. Therefore
it's sufficient to check for large enough data received.