mlx4: Add XDP frame size and adjust max XDP MTU

The mlx4 drivers size of memory backing the RX packet is stored in
frag_stride. For XDP mode this will be PAGE_SIZE (normally 4096).
For normal mode frag_stride is 2048.

Also adjust MLX4_EN_MAX_XDP_MTU to take tailroom into account.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Cc: Saeed Mahameed <saeedm@mellanox.com>
Link: https://lore.kernel.org/bpf/158945341893.97035.2688142527052329942.stgit@firesoul

drivers/net/ethernet/mellanox/mlx4/en_netdev.c

@@ -51,7 +51,8 @@
 #include "en_port.h"
 
 #define MLX4_EN_MAX_XDP_MTU ((int)(PAGE_SIZE - ETH_HLEN - (2 * VLAN_HLEN) - \
-				   XDP_PACKET_HEADROOM))
+				XDP_PACKET_HEADROOM -			    \
+				SKB_DATA_ALIGN(sizeof(struct skb_shared_info))))
 
 int mlx4_en_setup_tc(struct net_device *dev, u8 up)
 {

drivers/net/ethernet/mellanox/mlx4/en_rx.c

@@ -683,6 +683,7 @@ int mlx4_en_process_rx_cq(struct net_device *dev, struct mlx4_en_cq *cq, int bud
 	rcu_read_lock();
 	xdp_prog = rcu_dereference(ring->xdp_prog);
 	xdp.rxq = &ring->xdp_rxq;
+	xdp.frame_sz = priv->frag_info[0].frag_stride;
 	doorbell_pending = 0;
 
 	/* We assume a 1:1 mapping between CQEs and Rx descriptors, so Rx