ikev1: Move fragment generation to message_t

conf/options/charon.opt

@@ -85,9 +85,10 @@ charon.flush_auth_cfg = no
 	this might conflict with plugins that later need access to e.g. the used
 	certificates.
 
-charon.fragment_size = 512
-	Maximum size (in bytes) of a sent fragment when using the proprietary IKEv1
-	fragmentation extension.
+charon.fragment_size = 0
+	Maximum size (complete IP datagram size in bytes) of a sent fragment when
+	using the proprietary IKEv1	fragmentation extension (0 for address family
+	specific default values). If specified this limit is used for IPv4 and IPv6.
 
 charon.group
 	Name of the group the daemon changes to after startup.