wifi.proto: add SoftApReturnCode enum

SoftAp startup returns a failure mode if it does not start.  This
additional information is useful in determining where we need to add
logging and retry logic to make SoftAp mode more reliable.  The
combination of Failure + failure reason is mapped to an enum defined for
wifi metrics.

Bug: 30899122
Test: checked WifiMetricsProto.java for the enum
Test: frameworks/base/wifi/tests/runtests.sh
Test: frameworks/opt/net/wifi/tests/wifitests/runtests.sh
Change-Id: I944e3e249d3be5738352b26a1d12139fdd50bf80

proto/src/wifi.proto

@@ -435,9 +435,28 @@ message SoftApDurationBucket {
 
 // Number of occurrences of a soft AP session return code
 message SoftApReturnCodeCount {
-  // Return code of the soft AP session
-  optional int32 return_code = 1;
+
+  enum SoftApStartResult {
+
+    // SoftApManager return code unknown
+    SOFT_AP_RETURN_CODE_UNKNOWN = 0;
+
+    // SoftAp started successfully
+    SOFT_AP_STARTED_SUCCESSFULLY = 1;
+
+    // Catch all for failures with no specific failure reason
+    SOFT_AP_FAILED_GENERAL_ERROR = 2;
+
+    // SoftAp failed to start due to NO_CHANNEL error
+    SOFT_AP_FAILED_NO_CHANNEL = 3;
+  }
+
+  // Historical, no longer used for writing as of 01/2017.
+  optional int32 return_code = 1 [deprecated = true];
 
   // Occurences of this soft AP return code
   optional int32 count = 2;
+
+  // Result of attempt to start SoftAp
+  optional SoftApStartResult start_result = 3;
 }