rtlwifi: rtl8192ce: Fix loss of receive performance

Driver rtl8192ce when used with the RTL8188CE device would start at about
20 Mbps on a 54 Mbps connection, but quickly drop to 1 Mbps. One of the
symptoms is that the AP would need to retransmit each packet 4 of 5 times
before the driver would acknowledge it. Recovery is possible only by
unloading and reloading the driver. This problem was reported at
https://bugzilla.redhat.com/show_bug.cgi?id=770207.

The problem is due to a missing update of the gain setting.
Signed-off-by: Jingjun Wu <jingjun_wu@realsil.com.cn>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Stable <stable@vger.kernel.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rtlwifi/rtl8192c/dm_common.c

@@ -520,6 +520,10 @@ void rtl92c_dm_write_dig(struct ieee80211_hw *hw)
 		 dm_digtable.cur_igvalue, dm_digtable.pre_igvalue,
 		 dm_digtable.backoff_val);
 
+	dm_digtable.cur_igvalue += 2;
+	if (dm_digtable.cur_igvalue > 0x3f)
+		dm_digtable.cur_igvalue = 0x3f;
+
 	if (dm_digtable.pre_igvalue != dm_digtable.cur_igvalue) {
 		rtl_set_bbreg(hw, ROFDM0_XAAGCCORE1, 0x7f,
 			      dm_digtable.cur_igvalue);