Use string not StringPiece for knobs
Summary:
quicConfig is passed by value(https://fburl.com/codesearch/rydlyc2x), StringPiece doesn't do copy, resulting in junk values.
```
E1112 10:45:19.545003  1377 TransportKnobs.cpp:44] fail to parse knobs: json parse error on line 0 near |??
```
MODIFY
quic/state/TransportSettings.h
quic/state/TransportSettings.h
@@ -102,11 +102,11 @@ struct D6DConfig {
ProbeSizeRaiserType raiserType{ProbeSizeRaiserType::ConstantStep};
};
-// JSON-serialized transoprt knobs
+// JSON-serialized transport knobs
struct SerializedKnob {
uint64_t space;
uint64_t id;
- folly::StringPiece blob;
+ std::string blob;
};
struct TransportSettings {

Use string not StringPiece for knobs

Summary:
quicConfig is passed by value(https://fburl.com/codesearch/rydlyc2x), StringPiece doesn't do copy, resulting in junk values.

```
E1112 10:45:19.545003  1377 TransportKnobs.cpp:44] fail to parse knobs: json parse error on line 0 near |??
```

Reviewed By: yangchi

Differential Revision: D24928201

fbshipit-source-id: 57f391516689b3e5a4fa941d22f464c9830ad660