l1gprs: minor changes to l1gprs_handle_rts_ind()

* assert() the given TDMA Tn before accessing gprs->pdch[]
* do not check TDMA Fn, as there can be no RTS.ind for PTCCH/U
** unlike PTCCH/D, we send Access Bursts on PTCCH/U

Change-Id: Ie74d1c4123715d61875c4c956eb4a1ce97ed5f24
---
M src/shared/l1gprs.c
1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/src/shared/l1gprs.c b/src/shared/l1gprs.c
index 3294a42..1da2276 100644
--- a/src/shared/l1gprs.c
+++ b/src/shared/l1gprs.c
@@ -754,11 +754,11 @@
 	struct l1ctl_gprs_rts_ind *l1bi;
 	struct msgb *msg;
 
+	OSMO_ASSERT(tn < ARRAY_SIZE(gprs->pdch));
 	pdch = &gprs->pdch[tn];
 
 	LOGP_PDCH(pdch, LOGL_DEBUG,
-		  "Rx RTS.ind (%s, fn=%u, usf=%u)\n",
-		  ((fn % 104) == 12) ? "PTCCH" : "PDTCH",
+		  "Rx RTS.ind (PDTCH, fn=%u, usf=%u)\n",
 		  fn, usf);
 
 	l1gprs_check_pending_tbfs(gprs, fn);

