OsmoSGSN: configuration: Move pdp ctx specific CDR fields to its own table

Change-Id: I056f278b64ab426b9455b6a667abf2fe7fc94022
diff --git a/doc/manuals/chapters/configuration.adoc b/doc/manuals/chapters/configuration.adoc
index 22d28dd..c46a23c 100644
--- a/doc/manuals/chapters/configuration.adoc
+++ b/doc/manuals/chapters/configuration.adoc
@@ -198,7 +198,16 @@
 |lac|Location Area Code in which the MS was registered last
 |hlr|HLR of the subscriber
 |event|Possible events are explained below in <<sgsn-cdr-event>>
-|pdp|
+|===
+
+If the _event_ field describes a pdp context related action (starts with
+_pdp-_), then the following extra CSV fields are appended to the line:
+
+[[sgsn-cdr-pdp]]
+.Description of extra CSV fields for pdp context related events
+[options="header",cols="15%,85%"]
+|===
+|Field Name|Description
 |pdp_duration|duration of the PDP context so far
 |ggsn_addr|GGSN related to the PDP context
 |sgsn_addr|SGSN related to the PDP context