There are now many more reasons that virSocketAddrGetRange() could
fail, so it is much more informative to report the error there instead
of in the caller. (one of the two callers was previously assuming
success, which is almost surely safe based on the parsing that has
already happened to the config by that time, but it still is nicer to
account for an error "just in case")

Part of fix for: https://bugzilla.redhat.com/show_bug.cgi?id=985653