net: rswitch: Add unmap_addrs instead of dma address in each desc

If the driver would like to transmit a jumbo frame like 2KiB or more,
it should be split into multiple queues. In the near future, to support
this, add unmap_addrs array to unmap dma mapping address instead of dma
address in each TX descriptor because the descriptors may not have
the top dma address.

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