Drop existing tbf->ms() check condition

Since a while ago, tbf should always have an MS attached since its
creation, so there's no sense to check for it here.

Change-Id: If056a3fb83b43a48c2a6382fc30c6c81fe2b2651

src/tbf_ul.cpp

@@ -407,8 +407,7 @@ int gprs_rlcmac_ul_tbf::rcv_data_block_acknowledged(
 	gprs_rlcmac_rssi(this, rssi);
 
 	/* store measurement values */
-	if (ms())
-		ms_update_l1_meas(ms(), meas);
+	ms_update_l1_meas(ms(), meas);
 
 	uint32_t new_tlli = GSM_RESERVED_TMSI;
 	unsigned int block_idx;