Rely on APR to determine whether or not we have netinet/tcp.h. This test

requires a special work-around for IRIX 6.5, which will be in APR soon.
There is no need for it in Apache.

The include of netinet/tcp.h was removed from perchild.c and threaded.c.
They no longer seem to be needed there.

PR:		6459


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@88455 13f79535-47bb-0310-9956-ffa450edef68