net_sched: fix a compile warning in act_ife

Apparently ife_meta_id2name() is only called when
CONFIG_MODULES is defined.

This fixes:

net/sched/act_ife.c:251:20: warning: ‘ife_meta_id2name’ defined but not used [-Wunused-function]
 static const char *ife_meta_id2name(u32 metaid)
                    ^~~~~~~~~~~~~~~~

Fixes: d3f24ba8 ("net sched actions: fix module auto-loading")
Cc: Roman Mashak <mrv@mojatatu.com>
Signed-off-by: NCong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sched/act_ife.c

@@ -248,6 +248,7 @@ static int ife_validate_metatype(struct tcf_meta_ops *ops, void *val, int len)
 	return ret;
 }
 
+#ifdef CONFIG_MODULES
 static const char *ife_meta_id2name(u32 metaid)
 {
 	switch (metaid) {
@@ -261,6 +262,7 @@ static const char *ife_meta_id2name(u32 metaid)
 		return "unknown";
 	}
 }
+#endif
 
 /* called when adding new meta information
  * under ife->tcf_lock for existing action