sfc: move rx_rss_context_exclusive into struct efx_mcdi_filter_table

It's both set and used solely by mcdi_filters.c, so there's no reason
 for it to be in ef10-specific nic_data.

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