wifi(interface): Add/Correct docstring params

Changes in the CL:
1. Add missing docstring params in the HIDL interface.
2. Reword some method docs. Occurences of "will" is replaced
by "must" (based on comments received on supplicant HIDL interface:
go/aog/275115).
3. Add onFailure callbacks for all the methods and added docstrings for
them.

Bug: 31352200
Test: mmma -j32 hardware/interfaces/wifi/1.0
Change-Id: Ib7152625851023d6244f742bb77a8fdc0829e00d
diff --git a/wifi/1.0/IWifi.hal b/wifi/1.0/IWifi.hal
index 1feeb2a..d1311f5 100644
--- a/wifi/1.0/IWifi.hal
+++ b/wifi/1.0/IWifi.hal
@@ -28,8 +28,12 @@
   /**
    * Requests notifications of significant events for the HAL. Multiple calls to
    * this must register multiple callbacks each of which must receive all
-   * events. IWifiEventCallback registration must be independent of the state
-   * of the rest of the HAL and must persist though stops/starts.
+   * events. |IWifiEventCallback| object registration must be independent of the
+   * state of the rest of the HAL and must persist though stops/starts. These
+   * objects must be deleted when the corresponding client process is dead.
+   *
+   * @param callback An instance of the |IWifiEventCallback| HIDL interface
+   *        object.
    */
   @entry
   @callflow(next={"*"})
@@ -37,6 +41,8 @@
 
   /**
    * Get the current state of the HAL.
+   *
+   * @return started true if started, false otherwise.
    */
   isStarted() generates (bool started);