net: bridge: multicast: use the port group to port context helper

We need to use the new port group to port context helper in places where
we cannot pass down the proper context (i.e. functions that can be
called by timers or outside the packet snooping paths).

Signed-off-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>