Gap.proto: Add documentation for link layer states

services/ble/Gap.proto

@@ -11,6 +11,14 @@ message Address
     bytes address = 1 [(bytes_size) = 6];
 }
 
+// Link layer states of a device in a Peripheral or Central role
+// Peripheral role states are standby, connected and advertising.
+// Central role states are standby, scanning, connected and initiating.
+// Allowed transitions are as follows.
+// 1. Every state can go to standby.
+// 2. Every state can be entered from standby except the connected state.
+// 3. Connected state can only be entered from advertising and initiating states.
+// For further details refer to Section 1.1, BLUETOOTH CORE SPECIFICATION Version 5.3 | Vol 6, Part B  
 message State
 {
     enum Event
@@ -167,27 +175,45 @@ service GapPeripheral
 {
     option (service_id) = 32;
 
+    // Allowed states: standby
     rpc Advertise(AdvertisementMode) returns (Nothing) { option (method_id) = 1; }
+
+    // Allowed states: advertising, connected
     rpc Standby(Nothing) returns (Nothing) { option (method_id) = 2; }
+
     rpc SetAdvertisementData(AdvertisementData) returns (Nothing) { option (method_id) = 3; }
     rpc SetScanResponseData(AdvertisementData) returns (Nothing) { option (method_id) = 4; }
     rpc SetAllowPairing(BoolValue) returns (Nothing) { option (method_id) = 5; }
     rpc SetSecurityMode(SecurityModeAndLevel) returns (Nothing) { option (method_id) = 6; }
     rpc SetIoCapabilities(IoCapabilities) returns (Nothing) { option (method_id) = 7; }
     rpc RemoveAllBonds(Nothing) returns (Nothing) { option (method_id) = 8; }
+
+    // Allowed states: advertising
     rpc GetResolvableAddress(Nothing) returns (Nothing) { option (method_id) = 9; }
 }
 
 service GapCentral
 {
     option (service_id) = 33;
 
+    // Allowed states: standby
     rpc StartDeviceDiscovery(Nothing) returns (Nothing) { option (method_id) = 1; }
+
+    // Allowed states: standby
     rpc StopDeviceDiscovery(Nothing) returns (Nothing) { option (method_id) = 2; }
+
+    // Allowed states: standby
     rpc Connect(ConnectionParameters) returns (Nothing) { option (method_id) = 3; }
+
+    // Allowed states: initiating???
     rpc CancelConnect(Nothing) returns (Nothing) { option (method_id) = 4; }
+
+    // Allowed states: connected
     rpc Disconnect(Nothing) returns (Nothing) { option (method_id) = 5; }
+
+    // Allowed states: connected
     rpc Pair(Nothing) returns (Nothing) { option (method_id) = 6; }
+
     rpc SetSecurityMode(SecurityModeAndLevel) returns (Nothing) { option (method_id) = 7; }
     rpc SetIoCapabilities(IoCapabilities) returns (Nothing) { option (method_id) = 8; }
     rpc AuthenticateWithPasskey(UInt32Value) returns (Nothing) { option (method_id) = 9; }