migration: fix use of TLS PSK credentials with a UNIX socket

migration: fix use of TLS PSK credentials with a UNIX socket

The migration TLS code has a check mandating that a hostname be
available when starting a TLS session. This is expected when using
x509 credentials, but is bogus for PSK and anonymous credentials
as neither involve hostname validation.

The TLS crdentials object gained suitable error reporting in the
case of TLS with x509 credentials, so there is no longer any need
for the migration code to do its own (incorrect) validation.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20220310171821.3724080-7-berrange@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>