qapi: Add missing union tag documentation

Low-hanging fruit, and except for StatsFilter, the only members of
these unions lacking documentation.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20240205074709.3613229-16-armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
diff --git a/qapi/sockets.json b/qapi/sockets.json
index 5e6af55..ef77792 100644
--- a/qapi/sockets.json
+++ b/qapi/sockets.json
@@ -178,6 +178,8 @@
 # Captures the address of a socket, which could also be a named file
 # descriptor
 #
+# @type: Transport type
+#
 # Note: This type is deprecated in favor of SocketAddress.  The
 #     difference between SocketAddressLegacy and SocketAddress is that
 #     the latter has fewer {} on the wire.