s390/hvc_iucv: fix broken Kconfig select statement

Select statements in Kconfig do not necessarily enable all required
dependencies and can lead to broken configs. This is also the case
for the "select IUCV" statement within HVC_IUCV:

warning: (HVC_IUCV) selects IUCV which has unmet direct
         dependencies (NET && S390)

Just add the missing "depends on NET" to avoid broken configs.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/tty/hvc/Kconfig

@@ -44,7 +44,7 @@ config HVC_RTAS
 
 config HVC_IUCV
 	bool "z/VM IUCV Hypervisor console support (VM only)"
-	depends on S390
+	depends on S390 && NET
 	select HVC_DRIVER
 	select IUCV
 	default y