MINOR: connection: use the control layer's init/close

MINOR: connection: use the control layer's init/close

In conn_ctrl_init() and conn_ctrl_close() we now use the control layer's
functions instead of manipulating the FD directly. This is safe since the
control layer is always present when done. Note that now we also adjust
the flag before calling the function to make things cleaner in case such
a layer would need to call the same functions again for any reason.