Return M_INVALID_PARAM instead of M_BAD_JSON when setting aliases (…

…#3297)

Part of #3223
(matrix-org/matrix-spec#1286)

(For `DELETE` we don't validate the alias, but just return a 404 if we
can't find it)

clientapi/routing/directory.go

@@ -55,7 +55,7 @@ func DirectoryRoom(
 	if err != nil {
 		return util.JSONResponse{
 			Code: http.StatusBadRequest,
-			JSON: spec.BadJSON("Room alias must be in the form '#localpart:domain'"),
+			JSON: spec.InvalidParam("Room alias must be in the form '#localpart:domain'"),
 		}
 	}
 
@@ -134,7 +134,7 @@ func SetLocalAlias(
 	if err != nil {
 		return util.JSONResponse{
 			Code: http.StatusBadRequest,
-			JSON: spec.BadJSON("Room alias must be in the form '#localpart:domain'"),
+			JSON: spec.InvalidParam("Room alias must be in the form '#localpart:domain'"),
 		}
 	}