Fix recv_pkt_region incorrect usage

The `recv_pkt_region` is set when processing a flood packet in `filterRecvFloodPacket`
but direct/non-flood packets would never pass through that function, so the pointer was
not cleared for them.

`sendFloodReply` would then later use it blindly, which meant that the response would
either inherit the region from the last flood packet, or refer to a non-initialised pointer
if no region floods had been received yet.

examples/simple_repeater/MyMesh.h

@@ -166,7 +166,7 @@ protected:
   }
 #endif
 
-  bool filterRecvFloodPacket(mesh::Packet* pkt) override;
+  mesh::DispatcherAction onRecvPacket(mesh::Packet* pkt) override;
 
   void onAnonDataRecv(mesh::Packet* packet, const uint8_t* secret, const mesh::Identity& sender, uint8_t* data, size_t len) override;
   int searchPeersByHash(const uint8_t* hash) override;