Make logging of rendezvous to private address quieter
In #8976 (moved), we blocked rendezvous from hidden services to private addresses.
But the warning is log_warn LD_REND, when arma wonders if it should be a protocol warning to avoid excessive logging on busy services:
log_warn(LD_REND, "%s on circ %u", err_msg, (unsigned)circuit->base_.n_circ_id);
There's also a whitespace issue we might as well fix while we're there:
if (err_msg_out) *err_msg_out = err_msg; else tor_free(err_msg);