rtlwifi: Fix large packet issue

An RX buffer is set to 9100 bytes to receive 8K AMSDU; however, an skb
of this size fails in the kernel.

Signed-off-by: Chaoming Li <chaoming_li@realsil.com.cn>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>