net: ethernet: ti: Fix return type of netcp_ndo_start_xmit()

In the Linux kernel, the following vulnerability has been resolved:

net: ethernet: ti: Fix return type of netcp_ndo_start_xmit()

With clang's kernel control flow integrity (kCFI, CONFIG_CFI_CLANG),

indirect call targets are validated against the expected function

pointer prototype to make sure the call target is valid to help mitigate

ROP attacks. If they are not identical, there is a failure at run time,

which manifests as either a kernel panic or thread getting killed. A

proposed warning in clang aims to catch these at compile time, which

reveals:

drivers/net/ethernet/ti/netcp_core.c:1944:21: error: incompatible function pointer types initializing 'netdev_tx_t (*)(struct sk_buff *, struct net_device *)' (aka 'enum netdev_tx (*)(struct sk_buff *, struct net_device *)') with an expression of type 'int (struct sk_buff *, struct net_device *)' [-Werror,-Wincompatible-function-pointer-types-strict]

.ndo_start_xmit = netcp_ndo_start_xmit,

^~~~~~~~~~~~~~~~~~~~

1 error generated.

->ndo_start_xmit() in 'struct net_device_ops' expects a return type of

'netdev_tx_t', not 'int'. Adjust the return type of

netcp_ndo_start_xmit() to match the prototype's to resolve the warning

and CFI failure.