flowbits: Allow support for flowbit ORing

flowbits: Allow support for flowbit ORing

This patch allows to OR multiple flowbits on isset and isnotset flowbit
actions.

e.g.
Earlier in order to check if either fb1 or fb2 was set, it was required
to write two rules,
```
alert ip any any -> any any (msg:\"Flowbit fb1 isset\"; flowbits:isset,fb1; sid:1;)
alert ip any any -> any any (msg:\"Flowbit fb2 isset\"; flowbits:isset,fb2; sid:2;)
```

now, the same can be achieved with
```
alert ip any any -> any any (msg:\"Flowbit fb2 isset\"; flowbits:isset,fb1|fb2; sid:23;)
```

This operator can be used to check if one of the many flowbits is set
and also if one of the many flowbits is not set.