sfc: Don't try to set filters with search depths we know won't work

The filter engine will time-out and ignore filters beyond
200-something hops.  We also need to avoid infinite loops in
efx_filter_search() when the table is full.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>