Fix memory leak in pbx_dundi

pbx_dundi added an io context without removing
it. This caused a memory leak when the module was
unloaded.

(closes ASTERISK-21718)
Reported by Corey Farrell
Patches:
	pbx_dundi-ast_io_remove.patch uploaded by Corey Farrell (License #5909)
........

Merged revisions 388376 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/11@388378 65c4cc65-6c06-0410-ace0-fbb531ad65f3

pbx/pbx_dundi.c

@@ -2169,7 +2169,7 @@ static void *network_thread(void *ignore)
 	   from the network, and queue them for delivery to the channels */
 	int res;
 	/* Establish I/O callback for socket read */
-	ast_io_add(io, netsocket, socket_read, AST_IO_IN, NULL);
+	int *socket_read_id = ast_io_add(io, netsocket, socket_read, AST_IO_IN, NULL);
 
 	while (!dundi_shutdown) {
 		res = ast_sched_wait(sched);
@@ -2184,6 +2184,7 @@ static void *network_thread(void *ignore)
 		check_password();
 	}
 
+	ast_io_remove(io, socket_read_id);
 	netthreadid = AST_PTHREADT_NULL;
 
 	return NULL;