Rename as_{dl,ul}_tbf -> tbf_as_{dl,ul}_tbf

Prefix the function accordingly to specify the input object.

Change-Id: I225568fe2cb5236817cdd9609354c24c66723606
diff --git a/src/tbf_dl.h b/src/tbf_dl.h
index 8160cf3..e0daf57 100644
--- a/src/tbf_dl.h
+++ b/src/tbf_dl.h
@@ -130,7 +130,7 @@
 struct gprs_rlcmac_dl_tbf *dl_tbf_alloc(struct gprs_rlcmac_bts *bts, struct GprsMs *ms,
 					int8_t use_trx, bool single_slot);
 
-struct gprs_rlcmac_dl_tbf *as_dl_tbf(struct gprs_rlcmac_tbf *tbf);
+struct gprs_rlcmac_dl_tbf *tbf_as_dl_tbf(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,