DOC: config: fix aliases for protocol prefixes "udp4@" and "udp6@"

It was mentioned that they are equivalent to "stream+ipv*@" while it's
the equivalent of "dgram+ipv*@".
diff --git a/doc/configuration.txt b/doc/configuration.txt
index 3bd7066..e5edd83 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -24130,14 +24130,14 @@
                                  method is forced to "datagram". Depending on
                                  the statement using this address, a port or
                                  port range can or must be specified.
-                                 It is considered as an alias of 'stream+ipv4@'.
+                                 It is considered as an alias of 'dgram+ipv4@'.
 
 'udp6@<address>[:port1[-port2]]' following <address> is always considered as
                                  an IPv6 address but socket type and transport
                                  method is forced to "datagram". Depending on
                                  the statement using this address, a port or
                                  port range can or must be specified.
-                                 It is considered as an alias of 'stream+ipv4@'.
+                                 It is considered as an alias of 'dgram+ipv4@'.
 
 'uxdg@<path>'    following string is considered as a unix socket <path> but
                  transport method is forced to "datagram". It is considered as