gsup: Deprecate field pdp_type in favour of pdp_type_nr and pdp_type_org

Having both fields in an uin16_t integer makes it difficult and
confusing for users for no good reason. Let's have separate fields for
each of them.

The new fields are defined so that they are ABI compatible with previous
uin16 field.

Change-Id: Ie31c6080c90e468c01186259f2c42621e39b5cc6
diff --git a/TODO-RELEASE b/TODO-RELEASE
index e1d365e..3a0c80c 100644
--- a/TODO-RELEASE
+++ b/TODO-RELEASE
@@ -16,3 +16,4 @@
 isdn      ADD				initial implementation of the V.110 Terminal Adapter
 gsm		ABI change		add T200 timer states to lapdm_datalink
 gsm		ABI change		add UI queue to struct lapdm_datalink
+gsm		ADD			gsup.h: struct osmo_gsup_pdp_info fields pdp_type_nr, pdp_type_org, deprecate pdp_type.