dyn PDCH: Cleanup of rsl_chan_activate_lchan() and users

Timing advance is stored inside lchan structure, so it is removed from
arguments. This is useful, if other actions are required prior calling
rsl_chan_activate_lchan. (like deactivating PDCH first)

The "shifted TA value" that is required by BS11 is now calculated inside
rsl_chan_activate_lchan and not by each user.

[Rebased by Holger. So some hunks were skipped as the patch
depended on Jolly's HO code]
diff --git a/openbsc/src/libbsc/abis_rsl.c b/openbsc/src/libbsc/abis_rsl.c
index d193078..d9fe92c 100644
--- a/openbsc/src/libbsc/abis_rsl.c
+++ b/openbsc/src/libbsc/abis_rsl.c
@@ -476,12 +476,13 @@
 #endif
 
 int rsl_chan_activate_lchan(struct gsm_lchan *lchan, uint8_t act_type,
-			    uint8_t ta, uint8_t ho_ref)
+			    uint8_t ho_ref)
 {
 	struct abis_rsl_dchan_hdr *dh;
 	struct msgb *msg;
 	int rc;
 	uint8_t *len;
+	uint8_t ta;
 
 	uint8_t chan_nr = gsm_lchan2chan_nr(lchan);
 	struct rsl_ie_chan_mode cm;
@@ -491,6 +492,12 @@
 	if (rc < 0)
 		return rc;
 
+	ta = lchan->rqd_ta;
+
+	/* BS11 requires TA shifted by 2 bits */
+	if (lchan->ts->trx->bts->type == GSM_BTS_TYPE_BS11)
+		ta <<= 2;
+
 	memset(&cd, 0, sizeof(cd));
 	gsm48_lchan2chan_desc(&cd, lchan);
 
@@ -1469,10 +1476,7 @@
 		gsm_lchant_name(lchan->type), gsm_chreq_name(chreq_reason),
 		rqd_ref->ra, rqd_ta);
 
-	/* BS11 requires TA shifted by 2 bits */
-	if (bts->type == GSM_BTS_TYPE_BS11)
-		rqd_ta <<= 2;
-	rsl_chan_activate_lchan(lchan, 0x00, rqd_ta, 0);
+	rsl_chan_activate_lchan(lchan, 0x00, 0);
 
 	return 0;
 }