Changes

tlv: Allow control over comprehension bit in COMPR_TLV_IE

This allows construction of a comprehension TLV with the bit set or
cleared. The default is comprehension=True to not break existing code.

```
>>> foo = Foo(decoded=b"2342", comprehension=True)
>>> bar = Foo(decoded=b"2342", comprehension=False)
```

Related: OS#6989
Change-Id: I9ca689b9b51152f3907ea470c7b42a0b12208459

tlv: Remove unused branch

0xff is checked in the first if statement and already raises a ValueError

Change-Id: Ia6a0656721a1fcaf5f16526fefe62c30b0ddb664