Advertised header table size is not used

Current H2 implementation doesn't use the advertised header table size.

To reproduce:
```
$ nghttp -nv -c 1024 https://localhost/
```

This fails with COMPRESSION_ERROR.

Todo:
- Update internal maximum header table size with advertised size (SETTINGS_HEADER_TABLE_SIZE).
- Send "Dynamic Table Size Update" in the beginning of a header block


