[mlr] send MLR.req for local multicast addresses (#5248)

This commit includes:

- Adding compile configurations necessary for MLR features
- Adding source/header files necessary for MLR features
- Send MLR.req for local MAs on ThreadNetif
  - At most one MLR.req is outstanding
  - Reregistration according to PBBR configuration
  - Renewing periods according to PBBR configuration
- BBRs receive MLR.req with minimal processing and send MLR.rsp
- Add a test to verify that MLR.req is sent for local MAs.

tests/scripts/thread-cert/node.py

@@ -727,6 +727,11 @@ class Node:
         self.send_command(cmd)
         self._expect('Done')
 
+    def del_ipmaddr(self, ipmaddr):
+        cmd = 'ipmaddr del %s' % ipmaddr
+        self.send_command(cmd)
+        self._expect('Done')
+
     def get_addrs(self):
         self.send_command('ipaddr')