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

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: 7de8eb0d9039 ("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>