add protocol repo as a submodule

+[submodule "protocol"]
+	path = protocol
+	url = git@github.com:livekit/protocol.git

@@ -55,7 +55,7 @@ ext {
             protobuf          : "3.15.1",
     ]
     generated = [
-            protoSrc: "$projectDir/../protocol",
+            protoSrc: "$projectDir/protocol",
     ]
     deps = [
     ]

+ Subproject commit 1dadf893095928a27ae47b63cdce74607c38f229