neighbour: use kvzalloc()/kvfree()

mm layer is providing convenient functions, we do not have
to work around old limitations.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Gilad Naaman <gnaaman@drivenets.com>
Reviewed-by: Joe Damato <jdamato@fastly.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20241022150059.1345406-1-edumazet@google.com


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