configure: Fix check for rte_config.h to handle cross-compilation.

configure: Fix check for rte_config.h to handle cross-compilation.

The check for rte_config.h in acinclude.m4 used AC_CHECK_FILE, but this
macro is intended to check for a file on the host system, not the build
system, which means that it fails unconditionally in a cross-compilation
environment.  However, the intended check here is for a header file,
which is part of the build system.  To check for part of the build system,
we can just use "test", so this commit makes that change.

Reported-by: Hemant Agrawal <hemant.agrawal@nxp.com>
Reported-at: https://mail.openvswitch.org/pipermail/ovs-dev/2017-March/329994.html
Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Darrell Ball <dlu998@gmail.com>