net: bridge: mcast: fix vlan port router deadlock

Before vlan/port mcast router support was added
br_multicast_set_port_router was used only with bh already disabled due
to the bridge port lock, but that is no longer the case and when it is
called to configure a vlan/port mcast router we can deadlock with the
timer, so always disable bh to make sure it can be called from contexts
with both enabled and disabled bh.

Fixes: 2796d846 ("net: bridge: vlan: convert mcast router global option to per-vlan entry")
Signed-off-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>