afscp: use closesocket when closing sockets

afscp: use closesocket when closing sockets

close() is not portable to platforms where a socket is
not a file descriptor.

Reviewed-on: http://gerrit.openafs.org/4620
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit cb6cd6484edc0e026fe15e11fe86b9dcf106568d)

Change-Id: I8131c788fdcceee330f66bb8b47f76324b1735b1
Reviewed-on: http://gerrit.openafs.org/5386
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>