otMeshDiagRouterInfo::mIp6AddrIterator field

A pointer to an iterator to go through the list of IPv6 addresses of the router. The pointer is valid only while `otMeshDiagRouterInfo` is valid. It can be used in `otMeshDiagGetNextIp6Address` to iterate through the IPv6 addresses. The pointer can be NULL when there was no request to discover IPv6 addresses (in `otMeshDiagDiscoverConfig`) or if the router did not provide the list.