control_packet::wire_data() returns std::string_view

Summary: related to T13332

Reviewers: ivica

Reviewed By: ivica

Subscribers: miljen, iljazovic

Differential Revision: https://repo.mireo.local/D27099

include/async_mqtt5/detail/control_packet.hpp

@@ -105,7 +105,7 @@ public:
 		return *this;
 	}
 
-	const std::string& wire_data() const {
+	std::string_view wire_data() const {
 		return *_packet;
 	}
 };