fib: Fix undef compile warning

net/core/fib_rules.c:26:7: warning: "CONFIG_IP_MULTIPLE_TABLES" is not defined, evaluates to 0 [-Wundef]
 #elif CONFIG_IP_MULTIPLE_TABLES
       ^~~~~~~~~~~~~~~~~~~~~~~~~

Fixes: 8b66a6fd ("fib: fix another fib_rules_ops indirect call wrapper problem")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-By: Brian Vazquez <brianvv@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/fib_rules.c

@@ -23,7 +23,7 @@
 #else
 #define INDIRECT_CALL_MT(f, f2, f1, ...) INDIRECT_CALL_1(f, f2, __VA_ARGS__)
 #endif
-#elif CONFIG_IP_MULTIPLE_TABLES
+#elif defined(CONFIG_IP_MULTIPLE_TABLES)
 #define INDIRECT_CALL_MT(f, f2, f1, ...) INDIRECT_CALL_1(f, f1, __VA_ARGS__)
 #else
 #define INDIRECT_CALL_MT(f, f2, f1, ...) f(__VA_ARGS__)