[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.

examples/common-switches.mk

@@ -61,6 +61,7 @@ endif
 LINK_RAW            ?= 0
 MAC_FILTER          ?= 0
 MLE_LONG_ROUTES     ?= 0
+MLR                 ?= 0
 MTD_NETDIAG         ?= 0
 MULTIPLE_INSTANCE   ?= 0
 OTNS                ?= 0
@@ -205,6 +206,10 @@ ifeq ($(MLE_LONG_ROUTES),1)
 COMMONCFLAGS                   += -DOPENTHREAD_CONFIG_MLE_LONG_ROUTES_ENABLE=1
 endif
 
+ifeq ($(MLR),1)
+COMMONCFLAGS                   += -DOPENTHREAD_CONFIG_MLR_ENABLE=1
+endif
+
 ifeq ($(MTD_NETDIAG),1)
 COMMONCFLAGS                   += -DOPENTHREAD_CONFIG_TMF_NETWORK_DIAG_MTD_ENABLE=1
 endif