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

The packet transmission itself is implemented by igc_xdp_xmit_zc() which
is called from igc_clean_tx_irq() when the ring has AF_XDP zero-copy
enabled. Likewise i40e and ice drivers, the transmission budget used is
the number of descriptors available on the ring.

A new tx buffer type is introduced to 'enum igc_tx_buffer_type' to
indicate the tx buffer uses memory from xsk pool so it can be properly
cleaned after transmission or when the ring is cleaned.

The I225 controller has only 4 Tx hardware queues so the main difference
between igc and other Intel drivers that support AF_XDP zero-copy is
that there is no tx ring dedicated exclusively to XDP. Instead, tx
rings are shared between the network stack and XDP, and netdev queue
lock is used to ensure mutual exclusion. This is the same approach
implemented to support XDP_TX and XDP_REDIRECT actions.
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>