GTP: CreatePDPContext: only use IMEISV IE when IMEISV is known

The IE is optional, but if it is present, it must be 11 byte long
containing a 8 byte IMEISV. If IMEI is unknown the SGSN
would add an empty IMEISV IE which is invalid.

Change-Id: I812af1e702e77214244f32ae65663c1a03b23962

src/sgsn/sgsn_libgtp.c

@@ -300,11 +300,14 @@ struct sgsn_pdp_ctx *sgsn_create_pdp_ctx(struct sgsn_ggsn_ctx *ggsn,
 		break;
 	}
 
-	/* include the IMEI(SV) */
-	pdp->imeisv_given = 1;
-	gsm48_encode_bcd_number(&pdp->imeisv.v[0], 8, 0, mmctx->imei);
-	pdp->imeisv.l = pdp->imeisv.v[0];
-	memmove(&pdp->imeisv.v[0], &pdp->imeisv.v[1], 8);
+	/* optional include the IMEI(SV) */
+	if (mmctx->imei[0] != '\0') {
+		memset(&pdp->imeisv.v[0], 0, 8);
+		pdp->imeisv_given = 1;
+		gsm48_encode_bcd_number(&pdp->imeisv.v[0], 8, 0, mmctx->imei);
+		pdp->imeisv.l = 8;
+		memmove(&pdp->imeisv.v[0], &pdp->imeisv.v[1], 8);
+	}
 
 	/* change pdp state to 'requested' */
 	pctx->state = PDP_STATE_CR_REQ;