Add the initial XDP support to the igc driver. For now, only XDP_PASS,
XDP_DROP, XDP_ABORTED actions are supported. Upcoming patches will add
support for the remaining XDP actions.

XDP configuration helpers are defined in a new file, igc_xdp.c. These
helpers are utilized in igc_main.c to implement the ndo_bpf callback.
XDP-related code that belongs to the driver's hot path is landed in
igc_main.c.

By default, the driver uses Rx buffers with 2 KB size. When XDP is
enabled, it uses larger buffers so we have enough space to accommodate
the headroom and tailroom required by XDP infrastructure. Also, the
driver doesn't support XDP functionality with frames that span over
multiple buffers so jumbo frames are not allowed for now.

The approach implemented follows the approach implemented in other Intel
drivers as much as possible for the sake of consistency across the
drivers.

Quick comment regarding igc_build_skb(): this patch doesn't touch it
because the function is never called. It seems its support is
incomplete/in progress. The function was added by commit 0507ef8a
("igc: Add transmit and receive fastpath and interrupt handlers") but
ring_uses_build_skb() always return False since the IGC_RING_FLAG_RX_
BUILD_SKB_ENABLED isn't set anywhere in the driver code.

This patch has been tested with the sample app "xdp1" located in
samples/bpf/ dir.
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>