resolve: fix reverse lookups of client connections with ConnectIPv6=no

resolve: fix reverse lookups of client connections with ConnectIPv6=no

We re-use the same helper function for both forward lookups
(when we want to connect to a peer server) and for validation of reverse
loopups (where we make a lookup on the hostname returned
by a reverse lookup on the IP address that connected).

Problem:

When ConnectIPv6=no, the forward lookup helper sets the adderss family
to AF_INET, and, if out client connected via ipv6, we fail to validate
the result.

Thus move the ConnectIPvX check out of the helper.