gsm_data_shared: introduce 'struct gsm_abis_mo'

... as a common wrapper around nm_attr and nm_state
diff --git a/openbsc/src/libbsc/bts_ipaccess_nanobts.c b/openbsc/src/libbsc/bts_ipaccess_nanobts.c
index 706712e..e756f2a 100644
--- a/openbsc/src/libbsc/bts_ipaccess_nanobts.c
+++ b/openbsc/src/libbsc/bts_ipaccess_nanobts.c
@@ -402,7 +402,7 @@
 		 * This code is here to make sure that on start
 		 * a TRX remains locked.
 		 */
-		int rc_state = trx->nm_state.administrative;
+		int rc_state = trx->mo.nm_state.administrative;
 		/* Patch ARFCN into radio attribute */
 		nanobts_attr_radio[5] &= 0xf0;
 		nanobts_attr_radio[5] |= trx->arfcn >> 8;