Fix re-joining to the disconnected Thread network

When the OpenThread interface is disconnected, the Thread stack
removes the addresses on that interface.  By the time WARM has a
chance to deal with the situation, the Weave ULA address is no longer
on the interface, and the LwIP call
`netif_remove_ip6_address_with_route` returns an error code.  In turn,
when WARM observes that the operation to remove the address fails, it
does not update the state accordingly.  When the device rejoins, WARM
(having failed to update the state), does not reassign the Weave ULA
address to the interface.  As a result, all the packets going out to
Weave addresses (and the service address in particular) are sent with
the Thread mesh-local address as the source address and thus fail to
be routed properly.  By squashing the error on remove, we enable the
WARM state machine to re-add the Weave ULA address on reattach, and
thus put all routing decisions back on their well-worn paths.

We adopt the same approach to handle the internal address on the
OpenThread netif.

Author: robszewczyk

src/adaptations/device-layer/LwIP/WarmSupport.cpp

@@ -132,6 +132,15 @@ PlatformResult AddRemoveHostAddress(InterfaceType inInterfaceType, const Inet::I
     else
     {
         lwipErr = netif_remove_ip6_address_with_route(netif, &ip6addr, inPrefixLength);
+        // There are two possible errors from netif_remove_ip6_address: ERR_ARG
+        // if call was made with wrong arguments, or ERR_VAL if the action could
+        // not be performed (e.g. the address was already removed).  We squash
+        // ERR_VAL, and return SUCCESS so that WARM can set its state correctly.
+        if (lwipErr == ERR_VAL)
+        {
+            WeaveLogProgress(DeviceLayer, "netif_remove_ip6_address_with_route: Already removed");
+            lwipErr = ERR_OK;
+        }
         err = System::MapErrorLwIP(lwipErr);
         if (err != WEAVE_NO_ERROR)
         {
@@ -311,6 +320,16 @@ PlatformResult AddRemoveThreadAddress(InterfaceType inInterfaceType, const Inet:
     else
     {
         otErr = otIp6RemoveUnicastAddress(ThreadStackMgrImpl().OTInstance(), &otAddress.mAddress);
+        // There are two possible errors from otIp6RemoveUnicastAddress:
+        // OT_ERROR_INVALID_ARGS if the address was a multicast address, and
+        // OT_ERROR_NOT_FOUND if the address does not exist on the thread
+        // interface.  We squash the OT_ERROR_NOT_FOUND so that WARM sets its
+        // state correctly.
+        if (otErr == OT_ERROR_NOT_FOUND)
+        {
+            WeaveLogProgress(DeviceLayer, "otIp6RemoveUnicastAddress: already removed");
+            otErr = OT_ERROR_NONE;
+        }
     }
 
     ThreadStackMgrImpl().UnlockThreadStack();
@@ -442,4 +461,3 @@ const char * WarmInterfaceTypeToStr(InterfaceType inInterfaceType)
 } // namespace DeviceLayer
 } // namespace Weave
 } // namespace nl
-