tun_alloc_skb() is currently calling sock_alloc_send_pskb()
forcing order-0 page allocations.

Switch to PAGE_ALLOC_COSTLY_ORDER, to increase max allocation size by 8x.

Also add logic to increase the linear part if needed.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Tahsin Erdogan <trdgn@amazon.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20230801205254.400094-3-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>