net: rswitch: Add jumbo frames handling 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,
add handling specific descriptor types F{START,MID,END}. However, such
jumbo frames will not happen yet because the maximum MTU size is still
default for now.

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