neighbour: Add hlist_node to struct neighbour

Add a doubly-linked node to neighbours, so that they
can be deleted without iterating the entire bucket they're in.

Signed-off-by: Gilad Naaman <gnaaman@drivenets.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20241107160444.2913124-2-gnaaman@drivenets.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>