Update dynamic auto MCS selection logic to align with reference table

- Adjusted MCS indices 24 to 31 to match spec table's modulation (BPSK to 64-QAM) and coding rates (1/2 to 5/6).
- Revised signal strength thresholds (-45 to -75 dBm) to reflect realistic SNR requirements for each modulation scheme.
- Preserved random signal generation logic using rand_int_smooth.
- Ensured consistency with the reference table's structure and parameters.

Author: dingsen-Greenhorn

vwifi.c

@@ -1489,15 +1489,31 @@ static int vwifi_get_station(struct wiphy *wiphy,
         pr_info("vwifi: Station %pM using manual MCS %d (%s, %s)\n", mac,
                 mcs_index, modulation, coding_rate);
     } else {
-        if (sinfo->signal > -50) {
+        if (sinfo->signal > -45) {
             mcs_index = 31;
             modulation = "64-QAM";
             coding_rate = "5/6";
-        } else if (sinfo->signal > -70 && sinfo->signal <= -50) {
+        } else if (sinfo->signal > -50 && sinfo->signal <= -45) {
+            mcs_index = 30;
+            modulation = "64-QAM";
+            coding_rate = "3/4";
+        } else if (sinfo->signal > -55 && sinfo->signal <= -50) {
+            mcs_index = 29;
+            modulation = "64-QAM";
+            coding_rate = "2/3";
+        } else if (sinfo->signal > -60 && sinfo->signal <= -55) {
             mcs_index = 28;
             modulation = "16-QAM";
             coding_rate = "3/4";
-        } else if (sinfo->signal > -90 && sinfo->signal <= -70) {
+        } else if (sinfo->signal > -65 && sinfo->signal <= -60) {
+            mcs_index = 27;
+            modulation = "16-QAM";
+            coding_rate = "1/2";
+        } else if (sinfo->signal > -70 && sinfo->signal <= -65) {
+            mcs_index = 26;
+            modulation = "QPSK";
+            coding_rate = "3/4";
+        } else if (sinfo->signal > -75 && sinfo->signal <= -70) {
             mcs_index = 25;
             modulation = "QPSK";
             coding_rate = "1/2";