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/utils/bs11_config.c b/openbsc/src/utils/bs11_config.c
index aa8c55d..41acd69 100644
--- a/openbsc/src/utils/bs11_config.c
+++ b/openbsc/src/utils/bs11_config.c
@@ -882,8 +882,8 @@
 		fprintf(stderr, "Unable to allocate gsm network\n");
 		exit(1);
 	}
-	g_bts = gsm_bts_alloc(gsmnet, GSM_BTS_TYPE_BS11, HARDCODED_TSC,
-				HARDCODED_BSIC);
+	g_bts = gsm_bts_alloc_register(gsmnet, GSM_BTS_TYPE_BS11, HARDCODED_TSC,
+					HARDCODED_BSIC);
 
 	rc = rs232_setup(serial_port, delay_ms, g_bts);
 	if (rc < 0) {