brlapi: Make client not limit themselves to MAXPACKETSIZE
brlapi: Make client not limit themselves to MAXPACKETSIZE

except when connected to a server version 8, which was enforcing it.

Here only two cases are at stake:

- set of key pairs to be (un)ignored: when connected to a server version
8, the client needs to split the request into pieces. Otherwise we
assume that the server limitation is far enough for any needs and just
make the request unlimited.
- tty path: the limitation of server version 8 has never been an issue in
practice. We can thus just make it unlimited.

brltty/brltty,brltty/brltty,brltty/brltty,brltty/brltty,brltty/brltty,brltty/brltty