split gsm_data.c in gsm_data_shared.c and gsm_data.c

This facilitates the use of gsm_data.c from osmo-bts
diff --git a/openbsc/src/libbsc/bsc_vty.c b/openbsc/src/libbsc/bsc_vty.c
index 37a1e2f..971cdf7 100644
--- a/openbsc/src/libbsc/bsc_vty.c
+++ b/openbsc/src/libbsc/bsc_vty.c
@@ -1442,8 +1442,8 @@
 		return CMD_WARNING;
 	} else if (bts_nr == gsmnet->num_bts) {
 		/* allocate a new one */
-		bts = gsm_bts_alloc(gsmnet, GSM_BTS_TYPE_UNKNOWN,
-				    HARDCODED_TSC, HARDCODED_BSIC);
+		bts = gsm_bts_alloc_register(gsmnet, GSM_BTS_TYPE_UNKNOWN,
+					     HARDCODED_TSC, HARDCODED_BSIC);
 	} else
 		bts = gsm_bts_num(gsmnet, bts_nr);