Typo in doc/bird.conf.example2: MB-BGP -> MP-BGP

[Hexhu]

Hi,

In https://gitlab.nic.cz/labs/bird/-/blob/master/doc/bird.conf.example2, the
comment says "This is an example configuration file for MB-BGP setting".
Shouldn't it be MP-BGP setting? From git blame at
https://gitlab.nic.cz/labs/bird/-/blame/master/doc/bird.conf.example2,
the commit message says "Doc: Add MP-BGP example config file".

It's quite trivial though 😂.

Best regards,
Hexhu