route/mdb: use nl_list_for_each_entry_safe() for destroying list in mdb_free_data()
route/mdb: use nl_list_for_each_entry_safe() for destroying list in mdb_free_data()

I think this was wrong before. We cannot use mdb_free_data() and
free the current element.

Use nl_list_for_each_entry_safe() and properly unlink the element.

greearb/libnl-ct,thom311/libnl,thom311/libnl,greearb/libnl-ct,thom311/libnl,greearb/libnl-ct