idpf: fix checksums set in idpf_rx_rsc()

idpf_rx_rsc() uses skb_transport_offset(skb) while the transport header
is not set yet.

This triggers the following warning for CONFIG_DEBUG_NET=y builds.

DEBUG_NET_WARN_ON_ONCE(!skb_transport_header_was_set(skb))

[   69.261620] WARNING: CPU: 7 PID: 0 at ./include/linux/skbuff.h:3020 idpf_vport_splitq_napi_poll (include/linux/skbuff.h:3020) idpf
[   69.261629] Modules linked in: vfat fat dummy bridge intel_uncore_frequency_tpmi intel_uncore_frequency_common intel_vsec_tpmi idpf intel_vsec cdc_ncm cdc_eem cdc_ether usbnet mii xhci_pci xhci_hcd ehci_pci ehci_hcd libeth
[   69.261644] CPU: 7 UID: 0 PID: 0 Comm: swapper/7 Tainted: G S      W          6.14.0-smp-DEV #1697
[   69.261648] Tainted: [S]=CPU_OUT_OF_SPEC, [W]=WARN
[   69.261650] RIP: 0010:idpf_vport_splitq_napi_poll (include/linux/skbuff.h:3020) idpf
[   69.261677] ? __warn (kernel/panic.c:242 kernel/panic.c:748)
[   69.261682] ? idpf_vport_splitq_napi_poll (include/linux/skbuff.h:3020) idpf
[   69.261687] ? report_bug (lib/bug.c:?)
[   69.261690] ? handle_bug (arch/x86/kernel/traps.c:285)
[   69.261694] ? exc_invalid_op (arch/x86/kernel/traps.c:309)
[   69.261697] ? asm_exc_invalid_op (arch/x86/include/asm/idtentry.h:621)
[   69.261700] ? __pfx_idpf_vport_splitq_napi_poll (drivers/net/ethernet/intel/idpf/idpf_txrx.c:4011) idpf
[   69.261704] ? idpf_vport_splitq_napi_poll (include/linux/skbuff.h:3020) idpf
[   69.261708] ? idpf_vport_splitq_napi_poll (drivers/net/ethernet/intel/idpf/idpf_txrx.c:3072) idpf
[   69.261712] __napi_poll (net/core/dev.c:7194)
[   69.261716] net_rx_action (net/core/dev.c:7265)
[   69.261718] ? __qdisc_run (net/sched/sch_generic.c:293)
[   69.261721] ? sched_clock (arch/x86/include/asm/preempt.h:84 arch/x86/kernel/tsc.c:288)
[   69.261726] handle_softirqs (kernel/softirq.c:561)

Fixes: 3a8845a ("idpf: add RX splitq napi poll support")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Alan Brady <alan.brady@intel.com>
Cc: Joshua Hay <joshua.a.hay@intel.com>
Cc: Willem de Bruijn <willemb@google.com>
Acked-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Link: https://patch.msgid.link/20250226221253.1927782-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: edumazet

drivers/net/ethernet/intel/idpf/idpf_txrx.c

@@ -3013,7 +3013,6 @@ static int idpf_rx_rsc(struct idpf_rx_queue *rxq, struct sk_buff *skb,
 	skb_shinfo(skb)->gso_size = rsc_seg_len;
 
 	skb_reset_network_header(skb);
-	len = skb->len - skb_transport_offset(skb);
 
 	if (ipv4) {
 		struct iphdr *ipv4h = ip_hdr(skb);
@@ -3022,6 +3021,7 @@ static int idpf_rx_rsc(struct idpf_rx_queue *rxq, struct sk_buff *skb,
 
 		/* Reset and set transport header offset in skb */
 		skb_set_transport_header(skb, sizeof(struct iphdr));
+		len = skb->len - skb_transport_offset(skb);
 
 		/* Compute the TCP pseudo header checksum*/
 		tcp_hdr(skb)->check =
@@ -3031,6 +3031,7 @@ static int idpf_rx_rsc(struct idpf_rx_queue *rxq, struct sk_buff *skb,
 
 		skb_shinfo(skb)->gso_type = SKB_GSO_TCPV6;
 		skb_set_transport_header(skb, sizeof(struct ipv6hdr));
+		len = skb->len - skb_transport_offset(skb);
 		tcp_hdr(skb)->check =
 			~tcp_v6_check(len, &ipv6h->saddr, &ipv6h->daddr, 0);
 	}