Fix auto tests build with gcc 4.7

Added #include <unistd.h> to tests/auto/network-settings.h,
so qtbase auto tests successfully build.
It is needed after the header dependency changes, part of gcc 4.7.

Change-Id: I76d1082f8454263f2c22c31a13aa3c1bf6a0c82f
Reviewed-by: Shane Kearns <shane.kearns@accenture.com>

tests/auto/network-settings.h

@@ -48,6 +48,7 @@
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <netinet/in.h>
+#include <unistd.h>
 #endif
 
 class QtNetworkSettings