selftests: net: bridge: add vlan mcast_startup_query_count/interval tests

Add tests which change the new per-vlan startup query count/interval
options and verify the proper number of queries are sent in the expected
interval.

TEST: Vlan mcast_startup_query_interval global option default value   [ OK ]
TEST: Vlan mcast_startup_query_count global option default value    [ OK ]
TEST: Vlan 10 mcast_startup_query_interval option changed to 100    [ OK ]
TEST: Vlan 10 mcast_startup_query_count option changed to 3         [ OK ]

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