BTS support: nokia/ericcson - use e1inp_ts->lapd

the lapd member has moved from the .driver.dahdi.lapd to the more
generic lapd location inside 'struct e1inp_ts'
diff --git a/openbsc/src/libbsc/bts_nokia_site.c b/openbsc/src/libbsc/bts_nokia_site.c
index fa8f43e..4b5c50f 100644
--- a/openbsc/src/libbsc/bts_nokia_site.c
+++ b/openbsc/src/libbsc/bts_nokia_site.c
@@ -105,10 +105,10 @@
 #endif
 
 			if (start)
-				lapd_sap_start(ts->driver.dahdi.lapd, link->tei,
+				lapd_sap_start(ts->lapd, link->tei,
 					       link->sapi);
 			else
-				lapd_sap_stop(ts->driver.dahdi.lapd, link->tei,
+				lapd_sap_stop(ts->lapd, link->tei,
 					      link->sapi);
 		}
 	}