change memset to modern C++

src/dpp/sslclient.cpp

@@ -229,7 +229,7 @@ void set_signal_handler(int signal)
 	struct sigaction sa;
 	sigaction(signal, nullptr, &sa);
 	if (sa.sa_flags == 0 && sa.sa_handler == nullptr) {
-		memset(&sa, 0, sizeof(sa));
+		sa = {};
 		sigaction(signal, &sa, nullptr);
 	}
 }