netfilter: conntrack: fix udp offload timeout sysctl

`nf_flowtable_udp_timeout` sysctl option is available only
if CONFIG_NFT_FLOW_OFFLOAD enabled. But infra for this flow
offload UDP timeout was added under CONFIG_NF_FLOW_TABLE
config option. So, if you have CONFIG_NFT_FLOW_OFFLOAD
disabled and CONFIG_NF_FLOW_TABLE enabled, the
`nf_flowtable_udp_timeout` is not present in sysfs.
Please note, that TCP flow offload timeout sysctl option
is present even CONFIG_NFT_FLOW_OFFLOAD is disabled.

I suppose it was a typo in commit that adds UDP flow offload
timeout and CONFIG_NF_FLOW_TABLE should be used instead.

Fixes: 975c5750 ("netfilter: conntrack: Introduce udp offload timeout configuration")
Signed-off-by: Volodymyr Mytnyk <volodymyr.mytnyk@plvision.eu>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_conntrack_standalone.c

@@ -823,7 +823,7 @@ static struct ctl_table nf_ct_sysctl_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_jiffies,
 	},
-#if IS_ENABLED(CONFIG_NFT_FLOW_OFFLOAD)
+#if IS_ENABLED(CONFIG_NF_FLOW_TABLE)
 	[NF_SYSCTL_CT_PROTO_TIMEOUT_UDP_OFFLOAD] = {
 		.procname	= "nf_flowtable_udp_timeout",
 		.maxlen		= sizeof(unsigned int),