net: ena: rss: store hash function as values and not bits

The device receives, stores and retrieves the hash function value as bits
and not as their enum value.

The bug:
* In ena_com_set_hash_function() we set
  cmd.u.flow_hash_func.selected_func to the bit value of rss->hash_func.
 (1 << rss->hash_func)
* In ena_com_get_hash_function() we retrieve the hash function and store
  it's bit value in rss->hash_func. (Now the bit value of rss->hash_func
  is stored in rss->hash_func instead of it's enum value)

The fix:
This commit fixes the issue by converting the retrieved hash function
values from the device to the matching enum value of the set bit using
ffs(). ffs() finds the first set bit's index in a word. Since the function
returns 1 for the LSB's index, we need to subtract 1 from the returned
value (note that BIT(0) is 1).

Fixes: 1738cd3 ("net: ena: Add a driver for Amazon Elastic Network Adapters (ENA)")
Signed-off-by: Sameeh Jubran <sameehj@amazon.com>
Signed-off-by: Arthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/amazon/ena/ena_com.c

@@ -2370,7 +2370,11 @@ int ena_com_get_hash_function(struct ena_com_dev *ena_dev,
 	if (unlikely(rc))
 		return rc;
 
-	rss->hash_func = get_resp.u.flow_hash_func.selected_func;
+	/* ffs() returns 1 in case the lsb is set */
+	rss->hash_func = ffs(get_resp.u.flow_hash_func.selected_func);
+	if (rss->hash_func)
+		rss->hash_func--;
+
 	if (func)
 		*func = rss->hash_func;