net: lan966x: Fix return type of lan966x_port_xmit

The ndo_start_xmit field in net_device_ops is expected to be of type
netdev_tx_t (*ndo_start_xmit)(struct sk_buff *skb, struct net_device *dev).

The mismatched return type breaks forward edge kCFI since the underlying
function definition does not match the function hook definition.

The return type of lan966x_port_xmit should be changed from int to
netdev_tx_t.
Reported-by: Dan Carpenter <error27@gmail.com>
Link: https://github.com/ClangBuiltLinux/linux/issues/1703
Cc: llvm@lists.linux.dev
Signed-off-by: Nathan Huckleberry <nhuck@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20220929182704.64438-1-nhuck@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/microchip/lan966x/lan966x_main.c

@@ -344,7 +344,8 @@ static void lan966x_ifh_set_timestamp(void *ifh, u64 timestamp)
 		IFH_POS_TIMESTAMP, IFH_LEN * 4, PACK, 0);
 }
 
-static int lan966x_port_xmit(struct sk_buff *skb, struct net_device *dev)
+static netdev_tx_t lan966x_port_xmit(struct sk_buff *skb,
+				     struct net_device *dev)
 {
 	struct lan966x_port *port = netdev_priv(dev);
 	struct lan966x *lan966x = port->lan966x;