rll_establish: When on a TCH always use the SACH for SAPI!=0

When we are on a TCH/H or TCH/F always use the SACH for SAPI!=0
for the establishment otherwise it will never be answered. This
can be tested by starting to page with a traffic channel and then
trying to submit the SMS.
diff --git a/openbsc/src/bsc_rll.c b/openbsc/src/bsc_rll.c
index e9d6f25..1551d94 100644
--- a/openbsc/src/bsc_rll.c
+++ b/openbsc/src/bsc_rll.c
@@ -80,8 +80,7 @@
 	/* If we are a TCH and not in signalling mode, we need to
 	 * indicate that the new RLL connection is to be made on the SACCH */
 	if ((lchan->type == GSM_LCHAN_TCH_F ||
-	     lchan->type == GSM_LCHAN_TCH_H) &&
-	    lchan->rsl_cmode != RSL_CMOD_SPD_SIGN)
+	     lchan->type == GSM_LCHAN_TCH_H) && sapi != 0)
 		link_id |= 0x40;
 
 	use_lchan(lchan);