bridge: mcast: give fast leave precedence over multicast router and querier

When fast leave is configured on a bridge port and an IGMP leave is
received for a group, the group is not deleted immediately if there is
a router detected or if multicast querier is configured.
Ideally the group should be deleted immediately when fast leave is
configured.

Signed-off-by: Satish Ashok <sashok@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>