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

docs/libcurl/opts/CURLINFO_LOCAL_PORT.md

@@ -35,6 +35,9 @@ connection done with this **curl** handle.
 If the connection was done using QUIC, the port number is a UDP port number,
 otherwise it is a TCP port number.
 
+If no connection was established or if the protocol does not use ports, -1
+is returned.
+
 # %PROTOCOLS%
 
 # EXAMPLE

docs/libcurl/opts/CURLINFO_PRIMARY_PORT.md

@@ -36,6 +36,11 @@ If a proxy was used for the most recent transfer, this is the port number of
 the proxy, if no proxy was used it is the port number of the most recently
 accessed URL.
 
+If the connection was done using QUIC, the port number is a UDP port number.
+
+If no connection was established or if the protocol does not use ports, -1
+is returned.
+
 # %PROTOCOLS%
 
 # EXAMPLE