ice: Interpret .set_channels() input differently

A bug occurs because a safety check guarding AF_XDP-related queues in
ethnl_set_channels(), does not trigger. This happens, because kernel and
ice driver interpret the ethtool command differently.

How the bug occurs:
1. ethtool -l <IFNAME> -> combined: 40
2. Attach AF_XDP to queue 30
3. ethtool -L <IFNAME> rx 15 tx 15
   combined number is not specified, so command becomes {rx_count = 15,
   tx_count = 15, combined_count = 40}.
4. ethnl_set_channels checks, if there are any AF_XDP of queues from the
   new (combined_count + rx_count) to the old one, so from 55 to 40, check
   does not trigger.
5. ice interprets `rx 15 tx 15` as 15 combined channels and deletes the
   queue that AF_XDP is attached to.

Interpret the command in a way that is more consistent with ethtool
manual [0] (--show-channels and --set-channels).

Considering that in the ice driver only the difference between RX and TX
queues forms dedicated channels, change the correct way to set number of
channels to:

ethtool -L <IFNAME> combined 10 /* For symmetric queues */
ethtool -L <IFNAME> combined 8 tx 2 rx 0 /* For asymmetric queues */

[0] https://man7.org/linux/man-pages/man8/ethtool.8.html

Fixes: 87324e74

 ("ice: Implement ethtool ops for channels")
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com>
Tested-by: Chandan Kumar Rout <chandanx.rout@intel.com>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com>
Acked-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>