Drop unneeded arg 'ta' in tbf_alloc_ul()

The function is simply setting the ta on the ms, so simply make sure ta
is set on callers before passing the ms object.

Change-Id: Iebb9c57f458690e045ddc45c800209ad8cf621e0
diff --git a/src/tbf.h b/src/tbf.h
index 5ebd2e8..2b4cf6d 100644
--- a/src/tbf.h
+++ b/src/tbf.h
@@ -347,7 +347,7 @@
 
 
 struct gprs_rlcmac_ul_tbf *tbf_alloc_ul(struct gprs_rlcmac_bts *bts, GprsMs *ms,
-					int8_t use_trx, uint32_t tlli, uint8_t ta);
+					int8_t use_trx, uint32_t tlli);
 
 struct gprs_rlcmac_ul_tbf *tbf_alloc_ul_tbf(struct gprs_rlcmac_bts *bts, GprsMs *ms, int8_t use_trx, bool single_slot);