Rename tbf_alloc_dl_tbf() -> dl_tbf_alloc()

Rename it so that it follows the usual prefix for the type it allocates.

Change-Id: I7d30a85fefaa61d100fbd51af4601a3cf7de2159
diff --git a/src/tbf.cpp b/src/tbf.cpp
index 5597ba4..6598067 100644
--- a/src/tbf.cpp
+++ b/src/tbf.cpp
@@ -694,7 +694,7 @@
 
 	bts_do_rate_ctr_inc(bts, CTR_TBF_REUSED);
 
-	new_tbf = tbf_alloc_dl_tbf(bts, ms(),
+	new_tbf = dl_tbf_alloc(bts, ms(),
 		this->trx->trx_no, false);
 
 	if (!new_tbf) {