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/handover_logic.c b/openbsc/src/libbsc/handover_logic.c
index 36a758b..22f9883 100644
--- a/openbsc/src/libbsc/handover_logic.c
+++ b/openbsc/src/libbsc/handover_logic.c
@@ -131,8 +131,7 @@
 	new_lchan->conn->ho_lchan = new_lchan;
 
 	/* FIXME: do we have a better idea of the timing advance? */
-	rc = rsl_chan_activate_lchan(new_lchan, RSL_ACT_INTER_ASYNC, 0,
-				     ho->ho_ref);
+	rc = rsl_chan_activate_lchan(new_lchan, RSL_ACT_INTER_ASYNC, ho->ho_ref);
 	if (rc < 0) {
 		LOGP(DHO, LOGL_ERROR, "could not activate channel\n");
 		new_lchan->conn->ho_lchan = NULL;