sfc: rework handling of (firmware) multicast chaining state

Store the mc_chaining bit in struct efx_mcdi_filter_table, so that common
 code in mcdi_filters.c doesn't need to get it from ef10-specific nic_data.
Also, probe the firmware workaround just before the call to
 efx_mcdi_filter_table_probe(), rather than in a random other part of the
 driver bringup, to ensure that (a) it gets probed in time and (b) it gets
 reprobed as necessary on resets, no matter how the surrounding code gets
 reorganised and reordered.

Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>