vty: add 'show rejected-bts'

Print IDs and IPs of recently rejected BTS devices. Example output:

OsmoBSC> show rejected-bts
Date                Site ID BTS ID IP
------------------- ------- ------ ---------------
2018-10-25 09:36:28    1234      0    192.168.1.37

Related: OS#2841
Change-Id: Iba3bfe8fc9432b7ae8f819df8bd71b35b3ec507e
diff --git a/include/osmocom/bsc/gsm_data.h b/include/osmocom/bsc/gsm_data.h
index 7c91e59..7897fea 100644
--- a/include/osmocom/bsc/gsm_data.h
+++ b/include/osmocom/bsc/gsm_data.h
@@ -1129,6 +1129,16 @@
 	uint8_t chan_load_avg; /* current channel load average in percent (0 - 100). */
 };
 
+/* One rejected BTS */
+struct gsm_bts_rejected {
+	/* list header in net->bts_rejected */
+	struct llist_head list;
+
+	uint16_t site_id;
+	uint16_t bts_id;
+	char ip[INET6_ADDRSTRLEN];
+	time_t time;
+};
 
 struct gsm_network *gsm_network_init(void *ctx);
 
@@ -1404,6 +1414,7 @@
 
 	unsigned int num_bts;
 	struct llist_head bts_list;
+	struct llist_head bts_rejected;
 
 	/* shall reference gsm_network_T[] */
 	struct T_def *T_defs;