bts, tbf: Separate functions for dl/ul tbf_by_tlli lookup

In the future we want to separate ul and dl tbf into different
classes that inherit from a common base.

Ticket: SYS#389
Sponsored-by: On-Waves ehf
diff --git a/src/bts.h b/src/bts.h
index aa68ed7..c83bb18 100644
--- a/src/bts.h
+++ b/src/bts.h
@@ -192,7 +192,8 @@
 	/** add paging to paging queue(s) */
 	int add_paging(uint8_t chan_needed, uint8_t *identity_lv);
 
-	gprs_rlcmac_tbf *tbf_by_tlli(uint32_t tlli, enum gprs_rlcmac_tbf_direction dir);
+	gprs_rlcmac_tbf *dl_tbf_by_tlli(uint32_t tlli);
+	gprs_rlcmac_tbf *ul_tbf_by_tlli(uint32_t tlli);
 	gprs_rlcmac_tbf *tbf_by_poll_fn(uint32_t fn, uint8_t trx, uint8_t ts);
 	gprs_rlcmac_tbf *tbf_by_tfi(uint8_t tfi, uint8_t trx, enum gprs_rlcmac_tbf_direction dir);
 
@@ -238,6 +239,7 @@
 	SBAController m_sba;
 	TimingAdvance m_ta;
 	struct rate_ctr_group *m_ratectrs;
+	gprs_rlcmac_tbf *tbf_by_tlli(uint32_t tlli, enum gprs_rlcmac_tbf_direction dir);
 
 private:
 	/* disable copying to avoid slicing */