[OpenThread] Disable IPv6 interface during erasing persistent info.

Apart from disabling Thread, and erasing Persistent Info, we should
disable the IPv6 interface as well and block receiving further
packets.
Otherwise, if we don't reboot the device after erasing Thread
persistent data, we can get a packet and as a result, it causes an
assert during processing AES_ECB
(because crypto keys have been removed).

Author: ArekBalysNordic

src/platform/OpenThread/GenericThreadStackManagerImpl_OpenThread.hpp

@@ -1212,6 +1212,7 @@ void GenericThreadStackManagerImpl_OpenThread<ImplClass>::_ErasePersistentInfo(v
     ChipLogProgress(DeviceLayer, "Erasing Thread persistent info...");
     Impl()->LockThreadStack();
     otThreadSetEnabled(mOTInst, false);
+    otIp6SetEnabled(mOTInst, false);
     otInstanceErasePersistentInfo(mOTInst);
     Impl()->UnlockThreadStack();
 }