s390/netiucv: Fix return type of netiucv_tx()
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 v6.0.16 by commit e7a849f740e3576e79cba403697e916f4c3a6f12. For more details please see the references link.