Remove interlink_sequence_nr which is unused.

[ bigeasy: split out from Eric's patch ].
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://patch.msgid.link/20240906132816.657485-3-bigeasy@linutronix.deSigned-off-by: Jakub Kicinski <kuba@kernel.org>