Packet filter cli option (#2523)

## Issue Addressed

N/A

## Proposed Changes

Adds a cli option to disable packet filter in `lighthouse bootnode`. This is useful in running local testnets as the bootnode bans requests from the same ip(localhost) if the packet filter is enabled.

boot_node/src/cli.rs

@@ -60,6 +60,11 @@ pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
                 .help("Discovery can automatically update the node's local ENR with an external IP address and port as seen by other peers on the network. \
                 This enables this feature.")
         )
+        .arg(
+            Arg::with_name("disable-packet-filter")
+                .long("disable-packet-filter")
+                .help("Disables discv5 packet filter. Useful for testing in smaller networks")
+        )
         .arg(
             Arg::with_name("network-dir")
             .value_name("NETWORK_DIR")