Use new stat item/ctr getter APIs

Generated with spatch:
"""
@@
expression E1, E2;
@@
- &E2->ctr[E1]
+ rate_ctr_group_get_ctr(E2, E1)
"""

"""
@@
expression E1, E2, E3;
@@
- E2->items[E1]
+ osmo_stat_item_group_get_item(E2, E1)
"""

Change-Id: I41297a8df68e28dfc6016330ac82b0ed5dd0ebc1
diff --git a/src/gb/gprs_bssgp_bss.c b/src/gb/gprs_bssgp_bss.c
index a066e91..8230d87 100644
--- a/src/gb/gprs_bssgp_bss.c
+++ b/src/gb/gprs_bssgp_bss.c
@@ -466,8 +466,8 @@
 	msgb_nsei(msg) = bctx->nsei;
 	msgb_bvci(msg) = bctx->bvci;
 
-	rate_ctr_inc(&bctx->ctrg->ctr[BSSGP_CTR_PKTS_OUT]);
-	rate_ctr_add(&bctx->ctrg->ctr[BSSGP_CTR_BYTES_OUT], msg->len);
+	rate_ctr_inc(rate_ctr_group_get_ctr(bctx->ctrg, BSSGP_CTR_PKTS_OUT));
+	rate_ctr_add(rate_ctr_group_get_ctr(bctx->ctrg, BSSGP_CTR_BYTES_OUT), msg->len);
 
 	return bssgp_ns_send(bssgp_ns_send_data, msg);
 }