Add CHANGES and release note for [GL #1879]

CHANGES

@@ -1,3 +1,8 @@
+6378.	[func]		The option to specify the number of UDP dispatches was
+			previously removed. An attempt to use the option now prints
+			a warning.
+			[GL #1879]
+
 6377.	[func]		Introduce 'dnssec-ksr', a DNSSEC tool to create
 			Key Signing Requests (KSRs) and Signed Key Responses
 			(SKRs). [GL #1128]

bin/named/main.c

@@ -949,6 +949,7 @@ parse_command_line(int argc, char *argv[]) {
 			break;
 		case 'U':
 			/* Obsolete.  No longer in use.  Ignore. */
+			named_main_earlywarning("option '-U' has been removed");
 			break;
 		case 'u':
 			named_g_username = isc_commandline_argument;

doc/notes/notes-current.rst

@@ -29,7 +29,8 @@ New Features
 Removed Features
 ~~~~~~~~~~~~~~~~
 
-- None.
+- The ``named`` command line option ``-U <n>``, which specified the number of UDP dispatches,
+  has been removed. Using it now prints a warning.  :gl:`#1879`
 
 Feature Changes
 ~~~~~~~~~~~~~~~