gprs_rlcmac_pdch: Don't access private members

This patch introduces methods to get ul and dl tbf by tfi and uses them
in gprs_rlcmac_sched.

Sponsored by: On-Waves ehf
diff --git a/src/bts.cpp b/src/bts.cpp
index 9003099..3ca3628 100644
--- a/src/bts.cpp
+++ b/src/bts.cpp
@@ -990,3 +990,17 @@
 
 	return rc;
 }
+
+struct gprs_rlcmac_tbf *gprs_rlcmac_pdch::ul_tbf_by_tfi(uint8_t tfi)
+{
+	if (tfi >= ARRAY_SIZE(ul_tbf))
+		return NULL;
+	return ul_tbf[tfi];
+}
+
+struct gprs_rlcmac_tbf *gprs_rlcmac_pdch::dl_tbf_by_tfi(uint8_t tfi)
+{
+	if (tfi >= ARRAY_SIZE(dl_tbf))
+		return NULL;
+	return dl_tbf[tfi];
+}