tbf: Pass the MS object around instead of old_tbf

Currently the old TBF (either uplink or downlink) is passed around at
TBF allocation mainly to get information about the MS. To implement
more complex allocation algorithms, the MS object itself will be
needed anyway.

This commit replaces the old_tbf arguments by MS object arguments.

Sponsored-by: On-Waves ehf
diff --git a/src/bts.cpp b/src/bts.cpp
index 4ca53d5..8e56543 100644
--- a/src/bts.cpp
+++ b/src/bts.cpp
@@ -894,7 +894,7 @@
 
 		/* This call will register the new TBF with the MS on success */
 		tbf_alloc_ul(bts_data(), tbf->trx->trx_no, tbf->ms_class(),
-			tbf->tlli(), tbf->ta(), tbf);
+			tbf->tlli(), tbf->ta(), tbf->ms());
 
 		/* schedule uplink assignment */
 		tbf->ul_ass_state = GPRS_RLCMAC_UL_ASS_SEND_ASS;