rtlwifi: Use 6 bits as sequence number of TX report

In new design, SW_DEFINE[1:0] of tx desc are used by firmware, and the TX
report only contains SW_DEFINE[7:0]. To satisfy with all cases, driver uses
SW_DEFINE[7:2] as sequence number.
Besides, the format of tx report have been changed, so a new flag
RTL_SPEC_EXT_C2H is used to access report.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>