Expose the default for channel_binding in PQconndefaults().

If there's a static default value for a connection option,
it should be shown in the PQconninfoOptions array.

Daniele Varrazzo

Discussion: https://postgr.es/m/CA+mi_8Zo8Rgn7p+6ZRY7QdDu+23ukT9AvoHNyPbgKACxwgGhZA@mail.gmail.com

src/interfaces/libpq/fe-connect.c

@@ -215,7 +215,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 		"Database-Password-File", "", 64,
 	offsetof(struct pg_conn, pgpassfile)},
 
-	{"channel_binding", "PGCHANNELBINDING", NULL, NULL,
+	{"channel_binding", "PGCHANNELBINDING", DefaultChannelBinding, NULL,
 		"Channel-Binding", "", 8,	/* sizeof("require") == 8 */
 	offsetof(struct pg_conn, channel_binding)},