Small network adjustments (#1884)

## Issue Addressed

- Asymmetric pings - Currently with symmetric ping intervals, lighthouse nodes race each other to ping often ending in simultaneous ping connections. This shifts the ping interval to be asymmetric based on inbound/outbound connections
- Correct inbound/outbound peer-db registering - It appears we were accounting inbound as outbound and vice versa in the peerdb, this has been corrected
- Improved logging

There is likely more to come - I'll leave this open as we investigate further testnets

beacon_node/src/cli.rs

@@ -30,6 +30,13 @@ pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
         /*
          * Network parameters.
          */
+        .arg(
+            Arg::with_name("subscribe-all-subnets")
+                .long("subscribe-all-subnets")
+                .help("Subscribe to all subnets regardless of validator count. \
+                       This will also advertise the beacon node as being long-lived subscribed to all subnets.")
+                .takes_value(false),
+        )
         .arg(
             Arg::with_name("zero-ports")
                 .long("zero-ports")