r8169: allocate rx buffers using alloc_pages_node

We allocate 16kb per rx buffer, so we can avoid some overhead by using
alloc_pages_node directly instead of bothering kmalloc_node. Due to
this change buffers are page-aligned now, therefore the alignment check
can be removed.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Acked-by: Hayes Wang <hayeswang@realtek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>