BACKPORT: FROMGIT: netfilter: nfnetlink_log: always add a timestamp

Compared to all the other work we're already doing to deliver
an skb to userspace this is very cheap - at worse an extra
call to ktime_get_real() - and very useful.

(and indeed it may even be cheaper if we're running from other hooks)

(background: Android occasionally logs packets which
caused wake from sleep/suspend and we'd like to have
timestamps reliably associated with these events)

Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: Martin KaFai Lau <kafai@fb.com>
Cc: Florian Westphal <fw@strlen.de>
Signed-off-by: Maciej Żenczykowski <maze@google.com>
(cherry picked from commit 1d85594fd3e7e39e63b53b1bdc2d89db43b6ecd5 https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git main)
Bug: 276360178
Change-Id: I254a8d39cb7a232d47865a04cd6e0279606fa40e

net/netfilter/nfnetlink_log.c

@@ -587,9 +587,9 @@ __build_packet_message(struct nfnl_log_net *log,
 			goto nla_put_failure;
 	}
 
-	if (hooknum <= NF_INET_FORWARD && skb->tstamp) {
+	if (hooknum <= NF_INET_FORWARD) {
 		struct nfulnl_msg_packet_timestamp ts;
-		struct timespec64 kts = ktime_to_timespec64(skb->tstamp);
+		struct timespec64 kts = ktime_to_timespec64(skb->tstamp ?: ktime_get_real());
 		ts.sec = cpu_to_be64(kts.tv_sec);
 		ts.usec = cpu_to_be64(kts.tv_nsec / NSEC_PER_USEC);