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

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

src/sgsn/gprs_mm_state_iu_fsm.c

@@ -52,6 +52,9 @@ static void mmctx_change_gtpu_endpoints_to_sgsn(struct sgsn_mm_ctx *mm_ctx)
 		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));

src/sgsn/gprs_ranap.c

@@ -103,6 +103,8 @@ static int sgsn_ranap_rab_ass_resp(struct sgsn_mm_ctx *ctx, RANAP_RAB_SetupOrMod
 		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;
 	}