[net] Fix bug where AddrFetch connections would be counted as outbound full relay
Summary:
The desired logic is for us to only open feeler connections after we have hit the max count for outbound full relay connections. A short lived AddrFetch connection (previously called oneshot) could cause ThreadOpenConnections to miscount and mistakenly open a feeler instead of full relay.
Partial backport (15/19) of core PR19316:
https://github.com/bitcoin/bitcoin/pull/19316/commits/35839e963bf61d2da0d12f5b8cea74ac0e0fbd7b
Depends on D8724.
Test Plan:
ninja all check-all
Reviewers: #bitcoin_abc, majcosta
Reviewed By: #bitcoin_abc, majcosta
Differential Revision: https://reviews.bitcoinabc.org/D8725