net: rswitch: Use build_skb() for RX

If this hardware receives a jumbo frame like 2KiB or more, it will be
split into multiple queues. In the near future, to support this, use
build_skb() instead of netdev_alloc_skb_ip_align().

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>