tbf: Add tbf_as_{ul,dl}_tbf_const func helpers

This way we can easily get the subclass from the parent if the pointer
is const. Similar to what we already have for the opposite direction
{ul,dl}_tbf_as_tbf_const().

Change-Id: I35e650d13ecf3a5020d136e7d8d99837786503e2

src/tbf_dl.cpp

@@ -1272,3 +1272,11 @@ struct gprs_rlcmac_dl_tbf *tbf_as_dl_tbf(struct gprs_rlcmac_tbf *tbf)
 	else
 		return NULL;
 }
+
+const struct gprs_rlcmac_dl_tbf *tbf_as_dl_tbf_const(const struct gprs_rlcmac_tbf *tbf)
+{
+	if (tbf && tbf->direction == GPRS_RLCMAC_DL_TBF)
+		return static_cast<const gprs_rlcmac_dl_tbf *>(tbf);
+	else
+		return NULL;
+}

src/tbf_dl.h

@@ -130,6 +130,7 @@ struct gprs_rlcmac_dl_tbf *dl_tbf_alloc(struct gprs_rlcmac_bts *bts, struct Gprs
 					int8_t use_trx, bool single_slot);
 
 struct gprs_rlcmac_dl_tbf *tbf_as_dl_tbf(struct gprs_rlcmac_tbf *tbf);
+const struct gprs_rlcmac_dl_tbf *tbf_as_dl_tbf_const(const struct gprs_rlcmac_tbf *tbf);
 /* dispatch Unitdata.DL messages */
 int dl_tbf_handle(struct gprs_rlcmac_bts *bts,
 		  const uint32_t tlli, const uint32_t old_tlli,

src/tbf_ul.cpp

@@ -729,6 +729,14 @@ struct gprs_rlcmac_ul_tbf *tbf_as_ul_tbf(struct gprs_rlcmac_tbf *tbf)
 		return NULL;
 }
 
+const struct gprs_rlcmac_ul_tbf *tbf_as_ul_tbf_const(const struct gprs_rlcmac_tbf *tbf)
+{
+	if (tbf && tbf->direction == GPRS_RLCMAC_UL_TBF)
+		return static_cast<const gprs_rlcmac_ul_tbf *>(tbf);
+	else
+		return NULL;
+}
+
 void tbf_usf_timeout(struct gprs_rlcmac_ul_tbf *tbf)
 {
 	tbf->usf_timeout();

src/tbf_ul.h

@@ -136,6 +136,7 @@ struct gprs_rlcmac_ul_tbf *ul_tbf_alloc(struct gprs_rlcmac_bts *bts, struct Gprs
 void update_tbf_ta(struct gprs_rlcmac_ul_tbf *tbf, int8_t ta_delta);
 void set_tbf_ta(struct gprs_rlcmac_ul_tbf *tbf, uint8_t ta);
 struct gprs_rlcmac_ul_tbf *tbf_as_ul_tbf(struct gprs_rlcmac_tbf *tbf);
+const struct gprs_rlcmac_ul_tbf *tbf_as_ul_tbf_const(const struct gprs_rlcmac_tbf *tbf);
 void tbf_usf_timeout(struct gprs_rlcmac_ul_tbf *tbf);
 void ul_tbf_contention_resolution_start(struct gprs_rlcmac_ul_tbf *tbf);
 void ul_tbf_contention_resolution_success(struct gprs_rlcmac_ul_tbf *tbf);