This shouldn't be needed except for some corner cases, like if some
third party module does not limit their stuff properly, in S2S
or if channeldb contains some weird long entry or something.
`PROTOCTL BIGLINES` is set. This will allow us to do things more
efficiently and possibly raise some other limits in the future.
This 16k is the size of the complete line, including sender,
message tags, content and \r\n. Also, in server-to-server traffic
we now allow 30 parameters (MAXPARA*2).
The original input size limits for non-servers remain the same: the
complete line can be 4k+512, with the non-mtag portion limit set
at 512 bytes (including \r\n), and MAXPARA is still 15 as well.
* I chose 16k because I don't want to first raise it to like 8k
and then realize later that 16k would be better and raise it again.
* To receive BIGLINES in a command, you need to `CommandAdd()` with
flags `CMD_BIGLINES`, without it you still get regular 512 max.
This is so, because a lot of the code does not expect longer than
512 bytes lines or in parameters, so we can gradually change that
(where needed).
Bram Matthys