Kernel: Add Socket::set_role() and use it everywhere

Instead of having Socket subclasses write their role into Socket::m_role
directly, add a setter to do this.

Kernel/Net/UDPSocket.cpp

@@ -100,7 +100,7 @@ KResultOr<size_t> UDPSocket::protocol_send(const UserOrKernelBuffer& data, size_
 
 KResult UDPSocket::protocol_connect(FileDescription&, ShouldBlock)
 {
-    m_role = Role::Connected;
+    set_role(Role::Connected);
     set_connected(true);
     return KSuccess;
 }