Fabrice Bellet authored Feb 10, 2020 and Olivier Crête committed Feb 10, 2020

Removing lower-priority pairs to keep the conncheck list under a fixed
size (RFC 8445, sect 6.1.2.5) may accidently remove pairs that we want
to preserve, like succeeded and discovered pairs. We choose to only
remove pairs that are not engaged yet in the connection check
processing, those in frozen state.

Fixes #95