Define MOTD_MAXSIZE in default_options.h

[HansH111]

add MOTD_MAXSIZE 2000 in default_options.h instead of hard coded value (80 * 25) in svr_chansession.c

This way you can increase the value in local_options.h if really needed.

[mkj]

Is there really a good usecase for a motd larger than a minimal screen of text?

[HansH111]

Some groups are using it to display information about the system and applications and the backup schedule.
Sometimes I get more than 3600 bytes depending on number applications running on a server.
I currently have more than 140 servers where the motd information is broken off and people are complaining...

Now I have to modify the source code to change the size. this way I can set a larger MOTD_MAXSIZE in localoptions.h without changing the sourcecode....

[mkj]

Thanks. I've rebased it manually, github didn't want to in the PR.