[3.1.2 and older] birdc doesn't output the possible command expansions list

[Артём Варакса]

Hello,

I've observed an issue with `bird` 3.1.2 that is also reproducible in 
2.17.1, but not with 2.15.1 (i. e. a regression somewhere between 2.15.1 
and 2.17.1).

After starting the `bird` service, on 2.17.1 and newer:

 > # birdc
 > bird> show stat
 > Ambiguous command, possible expansions are:

On 2.15.1, the output is correct:

 > # birdc
 > bird> show stat
 > Ambiguous command, possible expansions are:
 > show status                                    Show router status
 > show static [<name>]                           Show details of static 
protocol
 > bird>

This was tested on ALT Linux (downstream issue: 
https://bugzilla.altlinux.org/54787). Per the maintainer, it's likely an 
issue in `bind` itself rather than the package, hence reporting here.

Thanks!