sfc: perform XDP processing on received packets

Adds a field to hold an attached xdp_prog, but never populates it (see
following patch).  Also, XDP_TX support is deferred to a later patch
in the series.

Track failures of xdp_rxq_info_reg() via per-queue xdp_rxq_info_valid
flags and a per-nic xdp_rxq_info_failed flag. The per-queue flags are
needed to prevent attempts to xdp_rxq_info_unreg() structs that failed
to register.  Possibly the API could be changed in the future to avoid
the need for these flags.

Signed-off-by: Charles McLachlan <cmclachlan@solarflare.com>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>