uac: fix wrong documentation regarding contact_addr database, empty string means skip, not dot

src/modules/uac/doc/uac_admin.xml

@@ -1619,7 +1619,7 @@ event_route[uac:reply] {
 			<listitem><para>
 			<emphasis>contact_addr</emphasis> - contact address to be used for this record
 			instead of reg_contact_addr module parameter, e.g.:, 192.168.0.125:5060. It can
-			be set to '.' (dot) to skip setting it and then reg_contact_addr modparam is used.
+			be set to '' (empty string) to skip setting it and then reg_contact_addr modparam is used.
 			</para></listitem>
 		</itemizedlist>
 		<itemizedlist>