selftests: net/bridge : add tests for per vlan snooping with stp state changes

Change ALL_TESTS definition to "test-per-line".

Add the test case of per vlan snooping with port stp state change to
forwarding and also vlan equivalent case in both bridge_igmp.sh and
bridge_mld.sh.

Signed-off-by: Yong Wang <yongwang@nvidia.com>
Reviewed-by: Andy Roulin <aroulin@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: David S. Miller <davem@davemloft.net>