setup_once.h: refactor inclusion of <unistd.h> and <sys/socket.h>

Inclusion of top two most included header files now done in setup_once.h

lib/hostip.c

@@ -22,9 +22,6 @@
 
 #include "setup.h"
 
-#ifdef HAVE_SYS_SOCKET_H
-#include <sys/socket.h>
-#endif
 #ifdef HAVE_NETINET_IN_H
 #include <netinet/in.h>
 #endif
@@ -34,9 +31,6 @@
 #ifdef HAVE_ARPA_INET_H
 #include <arpa/inet.h>
 #endif
-#ifdef HAVE_UNISTD_H
-#include <unistd.h>     /* for the close() proto */
-#endif
 #ifdef __VMS
 #include <in.h>
 #include <inet.h>