selftests: net: bridge: add test for mldv2 exc -> is_exclude report

The test checks for the following case:
   Router State  Report Received  New Router State     Actions
   EXCLUDE (X,Y)     IS_EX (A)     EXCLUDE (A-Y, Y*A)  (A-X-Y)=MALI
                                                       Delete (X-A)
                                                       Delete (Y-A)
                                                       Filter Timer=MALI

Signed-off-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>