tests: net: ipv6: move to new ztest API

Move net ipv6 tests to use new ztest API
1. Add rm_neighbor/rm_max_neighbors
2. Add a setup function including:
   add ifaddr_record to record ifaddr for teardown use
   add neighbor operations
3. Add a teardown fuction including:
   remove neighbor operations
   remove maddr
   set ifaddr_record to not used
4. add k_yield after rs message, so that ra_message can start receive
5. add leave_group, to restore to the original state after join_group
6. restore the mac address to original in test_change_ll_addr()
7. remove the addr/maddr to restore original in necessary test cases

Signed-off-by: Hu Zhenyu <zhenyu.hu@intel.com>