mlxsw: spectrum_switchdev: Do not remove mrouter port from MDB's ports list

When IGMP snooping is enabled on a bridge, traffic forwarded by an MDB
entry should be sent to both ports member in the MDB's ports list and
mrouter ports.

In case a port needs to be removed from an MDB's ports list, but this
port is also configured as an mrouter port, then do not update the
device so that it will continue to forward traffic through that port.

Fix a copy-paste error that checked that IGMP snooping is enabled twice
instead of checking the port's mrouter state.

Fixes: ded711c8 ("mlxsw: spectrum_switchdev: Consider mrouter status for mdb changes")
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reported-by: Colin King <colin.king@canonical.com>
Reviewed-by: Nogah Frankel <nogahf@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>