bts: Remove the global state gprs_rlcmac_trigger_downlink_assignment

Remove the global state from gprs_rlcmac_trigger_downlink_assignment
and walk up to the pcu_l1_if.cpp where I find the timeout handling
that should be part of the SBA and TBF functionality. In terms of
hierachies things start to be more clear.

There should be the BTS object. That holds the SBA and TBF Controllers
that can allocate TBFs and SBAs and will handle the timeout polling
for a BTS.
diff --git a/src/gprs_rlcmac.h b/src/gprs_rlcmac.h
index b8afdcd..760579b 100644
--- a/src/gprs_rlcmac.h
+++ b/src/gprs_rlcmac.h
@@ -183,7 +183,7 @@
 
 int gprs_rlcmac_tx_ul_ud(gprs_rlcmac_tbf *tbf);
 
-int gprs_rlcmac_poll_timeout(struct gprs_rlcmac_tbf *tbf);
+int gprs_rlcmac_poll_timeout(struct gprs_rlcmac_bts *bts, struct gprs_rlcmac_tbf *tbf);
 
 int gprs_rlcmac_sba_timeout(struct gprs_rlcmac_sba *sba);
 
@@ -198,10 +198,12 @@
 struct msgb *gprs_rlcmac_send_packet_downlink_assignment(
         struct gprs_rlcmac_tbf *tbf, uint32_t fn);
 
-void gprs_rlcmac_trigger_downlink_assignment(struct gprs_rlcmac_tbf *tbf,
+void gprs_rlcmac_trigger_downlink_assignment(struct gprs_rlcmac_bts *bts,
+	struct gprs_rlcmac_tbf *tbf,
         struct gprs_rlcmac_tbf *old_tbf, const char *imsi);
 
-int gprs_rlcmac_downlink_ack(struct gprs_rlcmac_tbf *tbf, uint8_t final,
+int gprs_rlcmac_downlink_ack(struct gprs_rlcmac_bts *bts,
+	struct gprs_rlcmac_tbf *tbf, uint8_t final,
         uint8_t ssn, uint8_t *rbb);
 
 int gprs_rlcmac_paging_request(uint8_t *ptmsi, uint16_t ptmsi_len,