Add feature flags for KernelTracers

Author: noboruma

proto/kernel_tracer.proto

@@ -8,6 +8,11 @@ import "common.proto";
 service KernelTracer {
     rpc GetKernelSupport(common.Empty) returns (KernelInfo);
     rpc GetMetrics      (common.Empty) returns (Metrics);
+    rpc GetFeatures     (common.Empty) returns (KernelFeatures);
+}
+
+enum Feature {
+    eBPF = 0;
 }
 
 message Metrics {
@@ -26,3 +31,7 @@ message KernelVersion {
 message KernelInfo {
     KernelVersion version = 1;
 }
+
+message KernelFeatures {
+    repeated Feature features = 1;
+}