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net: add skb drop reasons

Antoine Tenart requested to merge atenart/centos-stream-9:c9s/bz2059161/kfree_skb_reason into main

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2059161

Sync skb drop reasons with upstream to improve debuggability and visibility in
the net stack. This MR helps in understanding why a given packet is being
dropped.

One way of retrieving the skb drop reason is to hook to the kfree_skb tracepoint:

# perf record -e skb:kfree_skb -a sleep 10
# perf script
         swapper     0 [000] 45483.977088: skb:kfree_skb: skbaddr=0xffffa04859090f00 protocol=34525 location=0xffffffff9bc92940 reason: NOT_SPECIFIED  
         swapper     0 [000] 45485.792919: skb:kfree_skb: skbaddr=0xffffa04143757900 protocol=34525 location=0xffffffff9bbd84bb reason: TCP_INVALID_SEQUENCE

Signed-off-by: Antoine Tenart atenart@redhat.com

Edited by Antoine Tenart

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