The nng_dialer_close()
function closes the listener d.
This also closes any nng_pipe
objects that have
been created by the dialer.
Once this function returns, the dialer d and any of its resources
are deallocated.
Therefore it is an error to attempt to access d after
this function has returned.
(Attempts to do so will result in NNG_ECLOSED
errors.)
Dialers are implicitly closed when the socket they are associated with is closed.