sfc: fix TX channel offset when using legacy interrupts
This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v5.15.71 by commit 360910b88d1466a90644a4e0533803b594344a2b, it was introduced in version v5.15.47 by commit 06cb7e134f8f4a11b66f1dbeb5f237412a0aeedc. For more details please see the references link.