linux/netfilter.h: fix kernel-doc warnings

kernel-doc does not support DECLARE_PER_CPU(), so don't mark it with
kernel-doc notation.

One comment block is not kernel-doc notation, so just use
"/*" to begin the comment.

Quietens these warnings:

netfilter.h:493: warning: Function parameter or member 'bool' not described in 'DECLARE_PER_CPU'
netfilter.h:493: warning: Function parameter or member 'nf_skb_duplicated' not described in 'DECLARE_PER_CPU'
netfilter.h:493: warning: expecting prototype for nf_skb_duplicated(). Prototype was for DECLARE_PER_CPU() instead
netfilter.h:496: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
* Contains bitmask of ctnetlink event subscribers, if any.

Fixes: e7c8899f3e6f ("netfilter: move tee_active to core")
Fixes: fdf6491193e4 ("netfilter: ctnetlink: make event listener tracking global")
Signed-off-by: Randy Dunlap <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

include/linux/netfilter.h

···
 };
 extern const struct nfnl_ct_hook __rcu *nfnl_ct_hook;
 
-/**
+/*
  * nf_skb_duplicated - TEE target has sent a packet
  *
  * When a xtables target sends a packet, the OUTPUT and POSTROUTING
···
  */
 DECLARE_PER_CPU(bool, nf_skb_duplicated);
 
-/**
+/*
  * Contains bitmask of ctnetlink event subscribers, if any.
  * Can't be pernet due to NETLINK_LISTEN_ALL_NSID setsockopt flag.
  */