validates gossip addresses before sending pull-requests

IP addresses need to be validated before sending packets to them.
This commit, sends a ping packet to nodes before any pull requests.
Pull requests are then only sent to the nodes which have responded with
the correct hash of their respective ping packet.

core/src/cluster_info_metrics.rs

@@ -68,6 +68,7 @@ pub(crate) struct GossipStats {
     pub(crate) mark_pull_request: Counter,
     pub(crate) new_pull_requests: Counter,
     pub(crate) new_pull_requests_count: Counter,
+    pub(crate) new_pull_requests_pings_count: Counter,
     pub(crate) new_push_requests2: Counter,
     pub(crate) new_push_requests: Counter,
     pub(crate) new_push_requests_num: Counter,
@@ -242,6 +243,11 @@ pub(crate) fn submit_gossip_stats(stats: &GossipStats, gossip: &RwLock<CrdsGossi
             stats.pull_request_ping_pong_check_failed_count.clear(),
             i64
         ),
+        (
+            "new_pull_requests_pings_count",
+            stats.new_pull_requests_pings_count.clear(),
+            i64
+        ),
         (
             "generate_pull_responses",
             stats.generate_pull_responses.clear(),