hw/misc/ivshmem: Fix ivshmem_recv_msg() to also work on big endian systems

The "slow" ivshmem-tests currently fail when they are running on a
big endian host:

$ uname -m
ppc64
$ V=1 QTEST_QEMU_BINARY=x86_64-softmmu/qemu-system-x86_64 tests/ivshmem-test -m slow
/x86_64/ivshmem/single: OK
/x86_64/ivshmem/hotplug: OK
/x86_64/ivshmem/memdev: OK
/x86_64/ivshmem/pair: OK
/x86_64/ivshmem/server-msi: qemu-system-x86_64:
 -device ivshmem-doorbell,chardev=chr0,vectors=2: server sent invalid ID message
Broken pipe

The problem is that the server side code in ivshmem_server_send_one_msg()
correctly translates all messages IDs into little endian 64-bit values,
but the client side code in the ivshmem_recv_msg() function does not swap
the byte order back. Fix it by passing the value through le64_to_cpu().

Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <1504100343-26607-1-git-send-email-thuth@redhat.com>
Tested-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
