[][Refine TxD filling flow for Panther Ethernet driver]

[Description]
Change the TxD filling flow for Panther Ethernet driver.
This change mainly moves the action of writing
DDONE bit(txd3) to the mtk_tx_map() end.

[Resolved Issue]
If without this patch, NETSYS hardware might mistakenly
read old descriptor content in some corner cases.

[Release-log]
N/A

Change-Id: I196cdcd386000826b8bdc9e093e9784a6dd04c0b
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/5378402
1 file changed