Reduce the log level of tcpd_warn calls from ERR to WARNING.

This matches the name and avoids logging of warnings to console with
default syslog.conf, esp. getting rid of:
  warning: /etc/hosts.allow, line ..: can't verify hostname: \
     getaddrinfo(.., AF_INET) failed

contrib/tcp_wrappers/diag.c

@@ -52,7 +52,7 @@ void    VARARGS(tcpd_warn, char *, format)
     va_list ap;
 
     VASTART(ap, char *, format);
-    tcpd_diag(LOG_ERR, "warning", format, ap);
+    tcpd_diag(LOG_WARNING, "warning", format, ap);
     VAEND(ap);
 }