korina: do tx at the right position

Triggering TX before the write to the DMA status mask register leads to
transferring packets with maximum payload no matter what the actual
packet size is.
While here, also trigger RX scheduling after writing the DMA status mask
register, like it was in the original driver before it was sent
upstream.

Signed-off-by: Phil Sutter <n0-1@freewrt.org>
Acked-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: David S. Miller <davem@davemloft.net>