rtlwifi: Fix size of wireless mode variable

Smatch reports the following warning:

  CHECK   drivers/net/wireless/realtek/rtlwifi/rc.c
drivers/net/wireless/realtek/rtlwifi/rc.c:144 _rtl_rc_rate_set_series() warn: impossible condition '(wireless_mode == 256) => (0-255 == 256)'

This warning arises because commit acc6907b87a9 ("rtlwifi: Fix warning
from ieee80211_get_tx_rates() when using 5G") now checks the wireless
mode for WIRELESS_MODE_AC_ONLY (BIT(8)) in _rtl_rc_rate_set_series().
As a result, all quantities used to store the wireless mode must be u16.

This patch also reorders struct rtl_sta_info to save a little space.

Fixes: d76d65fd ("rtlwifi: fix broken VHT support")
Reported-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>