net: thunderx: Add XDP frame size

To help reviewers these are the defines related to RCV_FRAG_LEN

 #define DMA_BUFFER_LEN	1536 /* In multiples of 128bytes */
 #define RCV_FRAG_LEN	(SKB_DATA_ALIGN(DMA_BUFFER_LEN + NET_SKB_PAD) + \
			 SKB_DATA_ALIGN(sizeof(struct skb_shared_info)))

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Cc: Sunil Goutham <sgoutham@marvell.com>
Cc: Robert Richter <rrichter@marvell.com>
Link: https://lore.kernel.org/bpf/158945342402.97035.12649844447148990032.stgit@firesoul