Implement adding gws to multicast-group + Class-C scheduling config.

This makes it possible to add gateways to a multicast-group, which in
case configured will always be used for transmitting the multicast
downlinks.

This also moves the multicast class-c scheduling to the multicast-group
configuration. Options are delay between multiple gateways, or GPS time
synchronized transmission.

api/proto/api/gateway.proto

@@ -187,6 +187,9 @@ message ListGatewaysRequest {
     // Tenant ID (UUID) to filter gateways on.
     // To list all gateways as a global admin user, this field can be left blank.
     string tenant_id = 4;
+
+    // Multicast-group ID (UUID) to filter gateways on.
+    string multicast_group_id = 5;
 }
 
 message ListGatewaysResponse {

api/proto/api/multicast_group.proto

@@ -68,6 +68,21 @@ service MulticastGroupService {
         };
     }
 
+    // Add a gateway to the multicast group.
+    rpc AddGateway(AddGatewayToMulticastGroupRequest) returns (google.protobuf.Empty) {
+        option(google.api.http) = {
+            post: "/api/multicast-groups/{multicast_group_id}/gateways"
+            body: "*"
+        };
+    }
+
+    // Remove a gateway from the multicast group.
+    rpc RemoveGateway(RemoveGatewayFromMulticastGroupRequest) returns (google.protobuf.Empty) {
+        option(google.api.http) = {
+            delete: "/api/multicast-groups/{multicast_group_id}/gateways/{gateway_id}"
+        };
+    }
+
     // Add the given item to the multicast group queue.
     rpc Enqueue(EnqueueMulticastGroupQueueItemRequest) returns (EnqueueMulticastGroupQueueItemResponse) {
         option(google.api.http) = {
@@ -99,6 +114,19 @@ enum MulticastGroupType {
     CLASS_B = 1;
 }
 
+enum MulticastGroupSchedulingType {
+    // Delay.
+    // If multicast downlinks must be sent through multiple gateways, then
+    // these will be sent one by one with a delay between each gateway.
+    DELAY = 0;
+
+    // Time.
+    // If multicast downlinks must be sent through multiple gateways, then
+    // these will be sent simultaneously using GPS time synchronization.
+    // Note that this does require GPS time-synchronized LoRa gateways.
+    GPS_TIME = 1;
+}
+
 message MulticastGroup {
     // ID (UUID).
     // This will be generated automatically on create.
@@ -137,6 +165,9 @@ message MulticastGroup {
 
     // Ping-slot period (only for Class-B).
     uint32 class_b_ping_slot_period = 12;
+
+    // Scheduling type (only for Class-C).
+    MulticastGroupSchedulingType class_c_scheduling_type = 13;
 }
 
 message MulticastGroupListItem {
@@ -233,6 +264,22 @@ message RemoveDeviceFromMulticastGroupRequest {
     string dev_eui = 2;
 }
 
+message AddGatewayToMulticastGroupRequest {
+    // Multicast group ID.
+    string multicast_group_id = 1;
+
+    // Gateway ID (HEX encoded).
+    string gateway_id = 2;
+}
+
+message RemoveGatewayFromMulticastGroupRequest {
+    // Multicast group ID.
+    string multicast_group_id = 1;
+
+    // Gateway ID (HEX encoded).
+    string gateway_id = 2;
+}
+
 message MulticastGroupQueueItem {
     // Multicast group ID.
     string multicast_group_id = 1;