[][MAC80211][mt76][Add continuous TX support in testmode tx_frames]

[Description]
Add continuous TX support in testmode tx_frames
Enable continuous TX by setting tx_count=0xFFFFFFFF (UINT_MAX)

[Release-log]
N/A

Change-Id: I9e46fd3c7fabdbb832812d543bf5b6651e848a85
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/7267177
2 files changed