Kernel: Move socket role tracking to the Socket class itself

This is more logical and allows us to solve the problem of
non-blocking TCP sockets getting stuck in SocketRole::None.

The only complication is that a single LocalSocket may be shared
between two file descriptions (on the connect and accept sides),
and should have two different roles depending from which side
you look at it. To deal with it, Socket::role() is made a
virtual method that accepts a file description, and LocalSocket
internally tracks which FileDescription is the which one and
returns a correct role.

Kernel/Net/UDPSocket.cpp

@@ -81,6 +81,12 @@ int UDPSocket::protocol_send(const void* data, int data_length)
     return data_length;
 }
 
+KResult UDPSocket::protocol_connect(FileDescription&, ShouldBlock)
+{
+    m_role = Role::Connected;
+    return KSuccess;
+}
+
 int UDPSocket::protocol_allocate_local_port()
 {
     static const u16 first_ephemeral_port = 32768;