Bird 1.5 and 1.6 memory leak

[willy at mailoo.org]

> debian stretch, bird v 1.6.3-2 is rock solid
> 
> FWIW i saw zero leaks or issues on debian wheezy, jessie, devuan jessie 
> either.
> 
> on multiple rrs taking several million routes I am at:
> 
> birdc
> BIRD 1.6.3 ready.
> bird> show mem
> BIRD memory usage
> Routing tables:    126 MB
> Route attributes:   93 MB
> ROA tables:        112  B
> Protocols:         823 kB
> Total:             219 MB

As I said, the mem leak does not apppear in the `birdc show memory` command.
It is shown at the OS level, and is shown via the `free` command.
The leak was also present with v1.6.3  on ubuntu though.
Note that I don't have that much routes (~20), so the leak is not related to that IMO.

> alpine linux also works very well, no issues taking multiple full tables 
> on core/edge as well:
> 
> (host: core1)  (user: root)  (time= 11:23:53)
>   > ~ # birdc
> BIRD 1.6.0 ready.
> bird> show mem
> BIRD memory usage
> Routing tables:    182 MB
> Route attributes:  156 MB
> ROA tables:        192  B
> Protocols:         686 kB
> Total:             339 MB
> bird>

Unfortunately, switching to alpine or debian is not an option in my case.

Thank you for the input!