tbf: Just pass the MS object in reuse_tbf

Currently the MS will be searched based on the TLLI in resue_tbf().
Since the MS object is already known in the TBF when the TLLI is set,
it can just be passed to the new TBF.

This commit removes the call to update_ms() and just adds
new_tbf->set_ms(ms()) which will also work as expected if ms() == NULL.

Sponsored-by: On-Waves ehf
diff --git a/src/tbf_dl.cpp b/src/tbf_dl.cpp
index 5e4a51c..d2720ae 100644
--- a/src/tbf_dl.cpp
+++ b/src/tbf_dl.cpp
@@ -802,11 +802,11 @@
 		return;
 	}
 
+	new_tbf->set_ms(ms());
 	new_tbf->m_tlli = m_tlli;
 	new_tbf->m_tlli_valid = m_tlli_valid;
 	new_tbf->ta = ta;
 	new_tbf->assign_imsi(m_imsi);
-	new_tbf->update_ms(m_tlli, GPRS_RLCMAC_DL_TBF);
 
 	/* Copy over all data to the new TBF */
 	new_tbf->m_llc.put_frame(data, len);