bpf: make bnxt compatible w/ bpf_xdp_adjust_tail

w/ bpf_xdp_adjust_tail helper xdp's data_end pointer could be changed as
well (only "decrease" of pointer's location is going to be supported).
changing of this pointer will change packet's size.
for bnxt driver we will just calculate packet's length unconditionally
Acked-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NNikita V. Shirokov <tehnerd@tehnerd.com>
Acked-by: NMichael Chan <michael.chan@broadcom.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>

drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c

@@ -113,10 +113,10 @@ bool bnxt_rx_xdp(struct bnxt *bp, struct bnxt_rx_ring_info *rxr, u16 cons,
 	if (tx_avail != bp->tx_ring_size)
 		*event &= ~BNXT_RX_EVENT;
 
+	*len = xdp.data_end - xdp.data;
 	if (orig_data != xdp.data) {
 		offset = xdp.data - xdp.data_hard_start;
 		*data_ptr = xdp.data_hard_start + offset;
-		*len = xdp.data_end - xdp.data;
 	}
 	switch (act) {
 	case XDP_PASS: