Kernel: Record network statistics and expose as JSON

This is comprised of five small changes:

* Keep a counter for tx/rx packets/bytes per TCP socket
* Keep a counter for tx/rx packets/bytes per network adapter
* Expose that data in /proc/net_tcp and /proc/netadapters
* Convert /proc/netadapters to JSON
* Fix up ifconfig to read the JSON from netadapters

Kernel/Net/NetworkTask.cpp

@@ -334,6 +334,8 @@ void handle_tcp(const EthernetFrameHeader& eth, int frame_size)
         return;
     }
 
+    socket->record_incoming_data(ipv4_packet.payload_size());
+
 #ifdef TCP_DEBUG
     kprintf("handle_tcp: state=%s\n", TCPSocket::to_string(socket->state()));
 #endif