CVE-2022-50486: 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 netcpndostartxmit()

With clang's kernel control flow integrity (kCFI, CONFIGCFICLANG), 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/netcpcore.c:1944:21: error: incompatible function pointer types initializing 'netdevtxt ()(struct skbuff , struct netdevice )' (aka 'enum netdevtx ()(struct skbuff , struct netdevice )') with an expression of type 'int (struct skbuff , struct netdevice )' [-Werror,-Wincompatible-function-pointer-types-strict] .ndostartxmit = netcpndostartxmit, ^~~~~~~~~~~~~~~~~~~~ 1 error generated.

->ndostartxmit() in 'struct netdeviceops' expects a return type of 'netdevtxt', not 'int'. Adjust the return type of netcpndostartxmit() to match the prototype's to resolve the warning and CFI failure.