msh3: run again in its cfilter

- test 2500, single GET works
- test 2501, single POST stalls
- test 2502, multiple, sequential GETs each use a new connection since
  MsH3ConnectionGetState(qconn) no longer reports CONNECTED after one
  GET.

Closes #10204

lib/cf-socket.h

@@ -98,6 +98,14 @@ void Curl_sndbufset(curl_socket_t sockfd);
 #define Curl_sndbufset(y) Curl_nop_stmt
 #endif
 
+/**
+ * Assign the address `ai` to the Curl_sockaddr_ex `dest` and
+ * set the transport used.
+ */
+void Curl_sock_assign_addr(struct Curl_sockaddr_ex *dest,
+                           const struct Curl_addrinfo *ai,
+                           int transport);
+
 /**
  * Creates a cfilter that opens a TCP socket to the given address
  * when calling its `connect` implementation.