rtlwifi: Fix MAX MPDU of VHT capability

rtlwifi: Fix MAX MPDU of VHT capability

We must choose only one of VHT_CAP among
IEEE80211_VHT_CAP_MAX_MPDU_LENGTH_3895,
IEEE80211_VHT_CAP_MAX_MPDU_LENGTH_7991 and
IEEE80211_VHT_CAP_MAX_MPDU_LENGTH_11454.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Yan-Hsuan Chuang <yhchuang@realtek.com>
Cc: Birming Chiu <birming@realtek.com>
Cc: Shaofu <shaofu@realtek.com>
Cc: Steven Ting <steventing@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>