sshd: do not resolve refused client hostname

This is a compromise between POLA and practical reasoning. We don't
want to block the main server loop in an attempt to resolve. But we
need to keep the format of the logged message as is, for sake of
sshguard and other scripts. So let's print just the IP address twice,
this is what libwrap's refuse() would do if it failed to resolve.

Reviewed by: philip
PR: 269456
Differential revision: https://reviews.freebsd.org/D40069