tcp_sequence() uses two conditions to decide to drop a packet,
and we currently report generic TCP_INVALID_SEQUENCE drop reason.

Duplicates are common, we need to distinguish them from
the other case.

I chose to not reuse TCP_OLD_DATA, and instead added
TCP_OLD_SEQUENCE drop reason.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230719064754.2794106-1-edumazet@google.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>