net/smc: fix -Wmissing-prototypes warning when CONFIG_SYSCTL not set

when CONFIG_SYSCTL not set, smc_sysctl_net_init/exit
need to be static inline to avoid missing-prototypes
if compile with W=1.

Since __net_exit has noinline annotation when CONFIG_NET_NS
not set, it should not be used with static inline.
So remove the __net_init/exit when CONFIG_SYSCTL not set.

Fixes: 7de8eb0 ("net/smc: fix compile warning for smc_sysctl")
Signed-off-by: Dust Li <dust.li@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220309033051.41893-1-dust.li@linux.alibaba.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/smc/smc_sysctl.h

@@ -20,13 +20,13 @@ void __net_exit smc_sysctl_net_exit(struct net *net);
 
 #else
 
-int __net_init smc_sysctl_net_init(struct net *net)
+static inline int smc_sysctl_net_init(struct net *net)
 {
 	net->smc.sysctl_autocorking_size = SMC_AUTOCORKING_DEFAULT_SIZE;
 	return 0;
 }
 
-void __net_exit smc_sysctl_net_exit(struct net *net) { }
+static inline void smc_sysctl_net_exit(struct net *net) { }
 
 #endif /* CONFIG_SYSCTL */