s390/net: lcs: use IS_ENABLED() for kconfig detection

When CONFIG_ETHERNET=m or CONFIG_FDDI=m, lcs.s has build errors or
warnings:

../drivers/s390/net/lcs.c:40:2: error: #error Cannot compile lcs.c without some net devices switched on.
   40 | #error Cannot compile lcs.c without some net devices switched on.
../drivers/s390/net/lcs.c: In function 'lcs_startlan_auto':
../drivers/s390/net/lcs.c:1601:13: warning: unused variable 'rc' [-Wunused-variable]
 1601 |         int rc;

Solve this by using IS_ENABLED(CONFIG_symbol) instead of ifdef
CONFIG_symbol. The latter only works for builtin (=y) values
while IS_ENABLED() works for builtin or modular values.
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Alexandra Winter <wintera@linux.ibm.com>
Cc: Wenjia Zhang <wenjia@linux.ibm.com>
Cc: linux-s390@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/s390/net/lcs.c

@@ -36,7 +36,7 @@
 #include "lcs.h"
 
 
-#if !defined(CONFIG_ETHERNET) && !defined(CONFIG_FDDI)
+#if !IS_ENABLED(CONFIG_ETHERNET) && !IS_ENABLED(CONFIG_FDDI)
 #error Cannot compile lcs.c without some net devices switched on.
 #endif
 
@@ -1601,14 +1601,14 @@ lcs_startlan_auto(struct lcs_card *card)
 	int rc;
 
 	LCS_DBF_TEXT(2, trace, "strtauto");
-#ifdef CONFIG_ETHERNET
+#if IS_ENABLED(CONFIG_ETHERNET)
 	card->lan_type = LCS_FRAME_TYPE_ENET;
 	rc = lcs_send_startlan(card, LCS_INITIATOR_TCPIP);
 	if (rc == 0)
 		return 0;
 
 #endif
-#ifdef CONFIG_FDDI
+#if IS_ENABLED(CONFIG_FDDI)
 	card->lan_type = LCS_FRAME_TYPE_FDDI;
 	rc = lcs_send_startlan(card, LCS_INITIATOR_TCPIP);
 	if (rc == 0)
@@ -2139,13 +2139,13 @@ lcs_new_device(struct ccwgroup_device *ccwgdev)
 		goto netdev_out;
 	}
 	switch (card->lan_type) {
-#ifdef CONFIG_ETHERNET
+#if IS_ENABLED(CONFIG_ETHERNET)
 	case LCS_FRAME_TYPE_ENET:
 		card->lan_type_trans = eth_type_trans;
 		dev = alloc_etherdev(0);
 		break;
 #endif
-#ifdef CONFIG_FDDI
+#if IS_ENABLED(CONFIG_FDDI)
 	case LCS_FRAME_TYPE_FDDI:
 		card->lan_type_trans = fddi_type_trans;
 		dev = alloc_fddidev(0);