gsup.h: define newly added PCO IE

PCO - Protocol Configuration Options 3GPP TS 24.008 / 10.5.6.3.
The PCO will be used by the osmo-epdg to pass PCO internally.
The PCO will be passed towards to the PGW in the Session Request.

Related: OS#6369
Related: osmo-gsm-manuals.git Change-Id Id912ead4e1205f84a40af6505a5ddf050d1e086d
Change-Id: I0f9de90c7c67fe194b441a9d118eba70f09afb5e
diff --git a/TODO-RELEASE b/TODO-RELEASE
index 3e75184..01f7c41 100644
--- a/TODO-RELEASE
+++ b/TODO-RELEASE
@@ -20,3 +20,4 @@
 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.
 gsm		ABI change			gsup.h: Add field pdp_address in struct osmo_gsup_pdp_info shifts the struct, and in turn fields in struct osmo_gsup_message.
+gsm		ABI change		gsup.h: Add field pco in struct osmo_gsup_message. Length of the struct osmo_gsup_message increase.