MINOR: stats: report the number of active peers in "show info"

Peers are the last type of activity which can maintain a job present, so
it's important to report that such an entity is still active to explain
why the job count may be higher than zero. Here by "ActivePeers" we report
peers sessions, which include both established connections and outgoing
connection attempts.
diff --git a/include/types/global.h b/include/types/global.h
index 4b9d019..18cc63e 100644
--- a/include/types/global.h
+++ b/include/types/global.h
@@ -224,6 +224,7 @@
 extern int  actconn;            /* # of active sessions */
 extern int  listeners;
 extern int  jobs;               /* # of active jobs (listeners, sessions, open devices) */
+extern int  active_peers;       /* # of active peers (connection attempts and successes) */
 extern THREAD_LOCAL struct buffer trash;
 extern int nb_oldpids;          /* contains the number of old pids found */
 extern const int zero;
diff --git a/include/types/stats.h b/include/types/stats.h
index 8df8489..e59a240 100644
--- a/include/types/stats.h
+++ b/include/types/stats.h
@@ -291,6 +291,7 @@
 	INF_STOPPING,
 	INF_JOBS,
 	INF_LISTENERS,
+	INF_ACTIVE_PEERS,
 
 	/* must always be the last one */
 	INF_TOTAL_FIELDS