We're not currently setting skb->mac_header on ingress, and the netdev
core rx path expects it. Without it, we'll hit a warning on DEBUG_NETDEV
from commit 1e4033b53db4 ("net: skb_reset_mac_len() must check if
mac_header was set")

Initialise the mac_header to refer to the USB transport header.

Fixes: 0791c0327a6e ("net: mctp: Add MCTP USB transport driver")
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
---
 drivers/net/mctp/mctp-usb.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/mctp/mctp-usb.c b/drivers/net/mctp/mctp-usb.c
index 775a386d0aca1242e5d3c8a750c1d0825341caa6..36ccc53b17975912c7d310fe8d58eb91fe482732 100644
--- a/drivers/net/mctp/mctp-usb.c
+++ b/drivers/net/mctp/mctp-usb.c
@@ -183,6 +183,7 @@ static void mctp_usb_in_complete(struct urb *urb)
 		struct mctp_usb_hdr *hdr;
 		u8 pkt_len; /* length of MCTP packet, no USB header */
 
+		skb_reset_mac_header(skb);
 		hdr = skb_pull_data(skb, sizeof(*hdr));
 		if (!hdr)
 			break;

---
base-commit: 007a5ffadc4fd51739527f1503b7cf048f31c413
change-id: 20250829-mctp-usb-mac-header-7b6894234dbf

Best regards,
-- 
Jeremy Kerr <jk@codeconstruct.com.au>