igc: Enable RX via AF_XDP zero-copy

Add support for receiving packets via AF_XDP zero-copy mechanism.

Add a new flag to 'enum igc_ring_flags_t' to indicate the ring has
AF_XDP zero-copy enabled so proper ring setup is carried out during ring
configuration in igc_configure_rx_ring().

RX buffers can now be allocated via the shared pages mechanism (default
behavior of the driver) or via xsk pool (when AF_XDP zero-copy is
enabled) so a union is added to the 'struct igc_rx_buffer' to cover both
cases.

When AF_XDP zero-copy is enabled, rx buffers are allocated from the xsk
pool using the new helper igc_alloc_rx_buffers_zc() which is the
counterpart of igc_alloc_rx_buffers().

Likewise other Intel drivers that support AF_XDP zero-copy, in igc we
have a dedicated path for cleaning up rx irqs when zero-copy is enabled.
This avoids adding too many checks within igc_clean_rx_irq(), resulting
in a more readable and efficient code since this function is called from
the hot-path of the driver.

Signed-off-by: Andre Guedes <andre.guedes@intel.com>
Signed-off-by: Vedang Patel <vedang.patel@intel.com>
Signed-off-by: Jithu Joseph <jithu.joseph@intel.com>
Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Tested-by: Dvora Fuxbrumer <dvorax.fuxbrumer@linux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>