gtp: Set Direct Tunnel Flags DTI during UpdatePDPCtx

This is required as per TS 28.060 to tell the GGSN that the remote
Address/TEID it is receiving it's the one of the RNC.
Upon receiving a GTPU Error Indication, the GGSN knowing it's using
DirectTunnel, can then update the SGSN with UpdatePDPContextReq with
Direct Tunnel Flags DTI=1 EI=1 and then the SGSN can decide whether
reconfigure the Direct Tunnel or switch to 2-leg tunnel until the
connection with RNC/UE can be reestablished.

Depends: osmo-ggsn.git Change-Id Ia3e360a35d30858eab1e438dc2508fd756c2e22e
Related: SYS#5435
Change-Id: Iefe73eeea41df0c55db673194c9e9547504cbf0d
---
M TODO-RELEASE
M src/sgsn/gprs_mm_state_iu_fsm.c
M src/sgsn/gprs_ranap.c
3 files changed, 25 insertions(+), 0 deletions(-)

diff --git a/TODO-RELEASE b/TODO-RELEASE
index 0ed7189..79f557b 100644
--- a/TODO-RELEASE
+++ b/TODO-RELEASE
@@ -7,3 +7,4 @@
 # If any interfaces have been added since the last public release: c:r:a + 1.
 # If any interfaces have been removed or changed since the last public release: c:r:0.
 #library	what			description / commit summary line
+libgtp    >1.12.0   new field dir_tun_flags in struct pdp_t
diff --git a/src/sgsn/gprs_mm_state_iu_fsm.c b/src/sgsn/gprs_mm_state_iu_fsm.c
index c2e9c44..2bf3568 100644
--- a/src/sgsn/gprs_mm_state_iu_fsm.c
+++ b/src/sgsn/gprs_mm_state_iu_fsm.c
@@ -52,6 +52,9 @@
 		LOGMMCTXP(LOGL_INFO, mm_ctx, "Changing GTP-U endpoints %s -> %s\n",
 			  sgsn_gtp_ntoa(&pdp->lib->gsnlu),
 			  inet_ntop(AF_INET, &sgsn->cfg.gtp_listenaddr.sin_addr, buf, sizeof(buf)));
+		/* Disable Direct Tunnel Flags DTI. Other flags make no sense here, so also set to 0. */
+		pdp->lib->dir_tun_flags.l = 1;
+		pdp->lib->dir_tun_flags.v[0] = 0x00;
 		sgsn_pdp_upd_gtp_u(pdp,
 				   &sgsn->cfg.gtp_listenaddr.sin_addr,
 				   sizeof(sgsn->cfg.gtp_listenaddr.sin_addr));
diff --git a/src/sgsn/gprs_ranap.c b/src/sgsn/gprs_ranap.c
index 5e0d8ed..51954ce 100644
--- a/src/sgsn/gprs_ranap.c
+++ b/src/sgsn/gprs_ranap.c
@@ -103,6 +103,8 @@
 		LOGP(DRANAP, LOGL_DEBUG, "Updating TEID on RNC side from 0x%08x to 0x%08x\n",
 			pdp->lib->teid_own, tei);
 		pdp->lib->teid_own = tei;
+		pdp->lib->dir_tun_flags.l = 1;
+		pdp->lib->dir_tun_flags.v[0] = 0x01; /* Set DTI flag in Direct Tunnel Flags */
 		require_pdp_update = true;
 	}
 

