[SGSN] Deactivate SNDCP entity on PDP CTX DEACT CONFIRM

Otherwise we will end up leaking memory in the SNDCP layer...
diff --git a/openbsc/src/gprs/sgsn_libgtp.c b/openbsc/src/gprs/sgsn_libgtp.c
index 0eface3..b9c6605 100644
--- a/openbsc/src/gprs/sgsn_libgtp.c
+++ b/openbsc/src/gprs/sgsn_libgtp.c
@@ -287,6 +287,9 @@
 	DEBUGP(DGPRS, "Received DELETE PDP CTX CONF, cause=%d(%s)\n",
 		cause, get_value_string(gtp_cause_strs, cause));
 
+	/* Deactivate the SNDCP layer */
+	sndcp_sm_deactivate_ind(&pctx->mm->llme->lle[pctx->sapi], pctx->nsapi);
+
 	/* Confirm deactivation of PDP context to MS */
 	rc = gsm48_tx_gsm_deact_pdp_acc(pctx);