solos-pci: clean up pclose() function

 - Flush pending TX skbs from the queue rather than waiting for them all to
   complete (suggested by Krzysztof Mazur <krzysiek@podlesie.net>).
 - Clear ATM_VF_ADDR only when the PKT_PCLOSE packet has been submitted.
 - Don't clear ATM_VF_READY at all — vcc_destroy_socket() does that for us.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>