Rename as_{dl,ul}_tbf -> tbf_as_{dl,ul}_tbf

Prefix the function accordingly to specify the input object.

Change-Id: I225568fe2cb5236817cdd9609354c24c66723606
diff --git a/src/tbf_ul.h b/src/tbf_ul.h
index d69220d..301c52a 100644
--- a/src/tbf_ul.h
+++ b/src/tbf_ul.h
@@ -137,7 +137,7 @@
 #endif
 void update_tbf_ta(struct gprs_rlcmac_ul_tbf *tbf, int8_t ta_delta);
 void set_tbf_ta(struct gprs_rlcmac_ul_tbf *tbf, uint8_t ta);
-struct gprs_rlcmac_ul_tbf *as_ul_tbf(struct gprs_rlcmac_tbf *tbf);
+struct gprs_rlcmac_ul_tbf *tbf_as_ul_tbf(struct gprs_rlcmac_tbf *tbf);
 void tbf_usf_timeout(struct gprs_rlcmac_ul_tbf *tbf);
 bool ul_tbf_contention_resolution_done(const struct gprs_rlcmac_ul_tbf *tbf);
 struct osmo_fsm_inst *tbf_ul_ack_fi(const struct gprs_rlcmac_ul_tbf *tbf);