[][MAC80211][mt76][rework init txpower]

[Description]
Fix per-phy init txpower value, since each phy may have different chainmask.

[Release-log]
N/A

Change-Id: Ib8feb196d3fb7ce9a233e39c67f312846a23c47c
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/7826600
1 file changed