As described in the kdoc for .create_rxfh_context we are responsible
for populating the defaults. The core will not call .get_rxfh
for non-0 context.

The problem can be easily observed since Netlink doesn't currently
use the cache. Using netlink ethtool:

  $ ethtool -x eth0 context 1
  [...]
  RSS hash key:
  13:60:cd:60:14:d3:55:36:86:df:90:f2:96:14:e2:21:05:57:a8:8f:a5:12:5e:54:62:7f:fd:3c:15:7e:76:05:71:42:a2:9a:73:80:09:9c
  RSS hash function:
      toeplitz: on
      xor: off
      crc32: off

But using IOCTL ethtool shows:

  $ ./ethtool-old -x eth0 context 1
  [...]
  RSS hash key:
  00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00
  RSS hash function:
      Operation not supported

Fixes: 7964e788 ("net: ethtool: use the tracking array for get_rxfh on custom RSS contexts")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>