examples/telnet_server: add missing newline

The telnet example prints a line to the console, but it is not ended
with a newline. When using pyterm, the last line is then never shown as
it reads the console line by line and is waiting for the end of the
line.

This patch swaps use of `printf` for `puts` for the last line printed.
This means the missing newline character gets added. This is also done
to be consistent with the rest of the file, where puts is used whenever
possible instead of printf.

examples/telnet_server/main.c

@@ -79,7 +79,7 @@ int main(void)
 
     /* start shell */
     printf("All up, awaiting connection on port %u\n", CONFIG_TELNET_PORT);
-    printf("Local shell disabled");
+    puts("Local shell disabled");
     char line_buf[SHELL_DEFAULT_BUFSIZE];
     shell_run(NULL, line_buf, SHELL_DEFAULT_BUFSIZE);