bgp keepalive & hold timers

[Alexander Zubkov]

Hi,

Found interesting thing. If I set "keepalive time" for a BGP session,
this values is not modified after the hold time negotiations and as a
result I can get a BGP session with hold timer less than keepalive
timer and it will die due to hold timer expired after some time.
https://gitlab.nic.cz/labs/bird/-/blob/692055e3df6cc9f0d428d3b0dd8cdd8e825eb6f4/proto/bgp/packets.c#L908
I think more correct bahivour would be to close the BGP session with
unacceptable hold timer error in such case.