mod_cgid: In the handler, shut down the Unix socket (only for write)

mod_cgid: In the handler, shut down the Unix socket (only for write)
once we finish writing the request body to the cgi child process;
otherwise, the client doesn't hit EOF on stdin.  Small request bodies
worked without this change (for reasons I don't understand), but large
ones didn't.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86574 13f79535-47bb-0310-9956-ffa450edef68