Provide dummy impl of ap_proxy_connect_uds()

in case when APR_HAVE_SYS_UN_H is not defined.
Just returns APR_ENOTIMPL.

This helps symbol export/import handling on
Netware and also seems to be more correct,
because mod_proxy.h contains ap_proxy_connect_uds()
unconditionally.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1728650 13f79535-47bb-0310-9956-ffa450edef68