cosmetic: bs11: also use ts_is_tch()

Use the recently added ts_is_tch() function instead of an explicit switch to
determine TCH pchan types. This is a cosmetic change since the bs11 does not
support dynamic channels (which was the main motivator behind ts_is_tch()).

Change-Id: Idf8ce51c76a83210fe3d70e18c51bbaffebb8ad5
diff --git a/openbsc/src/libbsc/bts_siemens_bs11.c b/openbsc/src/libbsc/bts_siemens_bs11.c
index 160563b..c083b1e 100644
--- a/openbsc/src/libbsc/bts_siemens_bs11.c
+++ b/openbsc/src/libbsc/bts_siemens_bs11.c
@@ -400,15 +400,9 @@
 	if (is_ipaccess_bts(ts->trx->bts))
 		return;
 
-	switch (ts->pchan) {
-	case GSM_PCHAN_TCH_F:
-	case GSM_PCHAN_TCH_H:
+	if (ts_is_tch(ts))
 		abis_nm_conn_terr_traf(ts, e1l->e1_nr, e1l->e1_ts,
 					e1l->e1_ts_ss);
-		break;
-	default:
-		break;
-	}
 }
 
 static void nm_reconfig_trx(struct gsm_bts_trx *trx)