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

#define FILTER_CTL_SRCH_FUDGE_WILD 3

#define FILTER_CTL_SRCH_FUDGE_FULL 1

/* Hard maximum hop limit.  Hardware will time-out beyond 200-something.

 * We also need to avoid infinite loops in efx_filter_search() when the

 * table is full.

 */

#define FILTER_CTL_SRCH_MAX 200

struct efx_filter_table {

	u32		offset;		/* address of table relative to BAR */

	unsigned	size;		/* number of entries */

	incr = efx_filter_increment(key);

	for (depth = 1, filter_idx = hash & (table->size - 1);

	     depth <= FILTER_CTL_SRCH_MAX &&

		     test_bit(filter_idx, table->used_bitmap);

	     ++depth) {

		cmp = &table->spec[filter_idx];

	}

	if (!for_insert)

		return -ENOENT;

	if (depth > FILTER_CTL_SRCH_MAX)

		return -EBUSY;

found:

	*depth_required = depth;

	return filter_idx;