ip_quadruple/proxy: make port uint16_t

Make `port` member in these struct of type `uint16_t`.

add `uint8_t transport` to `struct ip_quadruple

Define TRNSPRT_NONE as 0. By assigning a valid transport only on a
successful connection, it is clear when the ip_quadruple members are
valid. Also, for transports not involving ports, the getinfos for
`CURLINFO_PRIMARY_PORT` and `CURLINFO_LOCAL_PORT` will now always return
-1.

Make all `transport` members and parameters of type `uint8_t`.

Document the return value of `CURLINFO_LOCAL_PORT` and
`CURLINFO_PRIMARY_PORT` in this regard. Add tests that writeout stats
report ports correctly.

Closes #19708

lib/setopt.c

@@ -1001,9 +1001,9 @@ static CURLcode setopt_long(struct Curl_easy *data, CURLoption option,
 #endif
 #ifndef CURL_DISABLE_PROXY
   case CURLOPT_PROXYPORT:
-    if((arg < 0) || (arg > 65535))
+    if((arg < 0) || (arg > UINT16_MAX))
       return CURLE_BAD_FUNCTION_ARGUMENT;
-    s->proxyport = (unsigned short)arg;
+    s->proxyport = (uint16_t)arg;
     break;
 
   case CURLOPT_PROXYAUTH: