[Example] Add a protocol version to reflect removing Shards:

* Not actually useful, because older clients won't speak this protocol
  version, and newer clients won't support Shards

src/xrpld/overlay/Peer.h

@@ -36,6 +36,7 @@ enum class ProtocolFeature {
     ValidatorListPropagation,
     ValidatorList2Propagation,
     LedgerReplay,
+    Shards,
 };
 
 /** Represents a peer connection in the overlay. */

src/xrpld/overlay/detail/PeerImp.cpp

@@ -502,6 +502,9 @@ PeerImp::supportsFeature(ProtocolFeature f) const
             return protocol_ >= make_protocol(2, 2);
         case ProtocolFeature::LedgerReplay:
             return ledgerReplayEnabled_;
+        case ProtocolFeature::Shards:
+            // Shards was removed in protocol version 2.3
+            return protocol_ < make_protocol(2, 3);
     }
     return false;
 }

src/xrpld/overlay/detail/ProtocolVersion.cpp

@@ -37,7 +37,8 @@ namespace ripple {
 constexpr ProtocolVersion const supportedProtocolList[]
 {
     {2, 1},
-    {2, 2}
+    {2, 2},
+    {2, 3}
 };
 // clang-format on